In The Chronicles of Narnia, a total of seven people were described as being practical, and three of them were called practical in a rather negative way.

JADIS

The children were now afraid that Jadis would have something to say to them about what had happened in the wood. As it turned out, however, she never mentioned it either then or afterwards. I think (and Digory thinks too) that her mind was of a sort which cannot remember that quiet place at all, and however often you took her there and however long you left her there, she would still know nothing about it. Now that she was left alone with the children, she took no notice of either of them. And that was like her too. In Charn she had taken no notice of Polly (till the very end) because Digory was the one she wanted to make use of. Now that she had Uncle Andrew, she took no notice of Digory. I expect most witches are like that. They are not interested in things or people unless they can use them; they are terribly practical. So there was silence in the room for a minute or two. But you could tell by the way Jadis tapped her foot on the floor that she was growing impatient. – from Chapter 6, “The Beginning of Uncle Andrew’s Troubles,” The Magician’s Nephew

From this quote about Jadis, being practical means only paying attention to someone if you wanted to use the person in one way or another. Jadis didn’t pay attention to Polly because she was using Digory. Later on, she didn’t pay attention to Digory either because she was using Uncle Andrew. She didn’t waste her time in noticing or paying attention to people who didn’t suit her purposes.

UNCLE ANDREW

We must now go back a bit and explain what the whole scene had looked like from Uncle Andrew’s point of view. It had not made at all the same impression on him as on the Cabby and the children. For what you see and hear depends a good deal on where you are standing: it also depends on what sort of person you are.

Ever since the animals had first appeared, Uncle Andrew had been shrinking further and further back into the thicket. He watched them very hard of course; but he wasn’t really interested in seeing what they were doing, only in seeing whether they were going to make a rush at him. Like the Witch, he was dreadfully practical. He simply didn’t notice that Aslan was choosing one pair out of every kind of beasts. All he saw, or thought he saw, was a lot of dangerous wild animals walking vaguely about. And he kept on wondering why the other animals didn’t run away from the big Lion. – from Chapter 9, “The Founding of Narnia,” The Magician’s Nephew

From this quote about Uncle Andrew, being practical means only paying attention to something that involves yourself and nothing more. Uncle Andrew missed the point of the entire creation (or “founding”) of Narnia simply because he was only concerned that that the animals wouldn’t attack him. He didn’t waste his time in noticing or paying attention to things that didn’t concern him directly.

ARSHEESH

Sometimes if Arsheesh was there Shasta would say, “O my Father, what is there beyond that hill?” And then if the fisherman was in a bad temper he would box Shasta’s ears and tell him to attend to his work. Or if he was in a peaceable mood he would say, “O my son, do not allow your mind to be distracted by idle questions. For one of the poets has said, `Application to business is the root of prosperity, but those who ask questions that do not concern them are steering the ship of folly towards the rock of indigence’.”

Shasta thought that beyond the hill there must be some delightful secret which his father wished to hide from him. In reality, however, the fisherman talked like this because he didn’t know what lay to the North. Neither did he care. He had a very practical mind. – from Chapter 1, “How Shasta Set Out on His Travels,” The Horse and His Boy

From this quote about Arsheesh, being practical means only paying attention to something that you already know about. He never concerned himself with the lands beyond, like the free North. He didn’t waste his time in noticing or paying attention to things that he wasn’t familar with.

Being practical isn’t all that bad though. In fact, there were four others who were mentioned as being practical, but not in the way that Jadis, Uncle Andrew and Arsheesh were.

DUFFLE AND THE STAG

Presently, however, two more practical people arrived in the little wood. One was a Red Dwarf whose name appeared to be Duffle. The other was a stag, a beautiful lordly creature with wide liquid eyes, dappled flanks and legs so thin and graceful that they looked as if you could break them with two fingers.

“Lion alive!” roared the Dwarf as soon as he had heard the news. “And if that’s so, why are we all standing still, chattering? Enemies at Anvard! News must be sent to Cair Paravel at once. The army must be called out. Narnia must go to the aid of King Lune.”

“Ah!” said the Hedgehog. “But you won’t find the High King at the Cair. He’s away to the North trouncing those giants. And talking of giants, neighbours, that puts me in mind -” 

“Who’ll take our message?” interrupted the Dwarf. “Anyone here got more speed than me?”

“I’ve got speed,” said the Stag. “What’s my message? How many Calormenes?”

“Two hundred: under Prince Rabadash. And -” But the Stag was already away – all four legs off the ground at once, and in a moment its white stern had disappeared among the remoter trees. – from Chapter 12, “Shasta in Narnia,” The Horse and His Boy

From this quote, being practical means doing what must be done. Upon learning of the coming army of Prince Rabadash, the other creatures didn’t exactly jump into action, but dawdled around chatting about it. Only Duffle, who took control of the situation, and the stag, who rushed to inform the High King, did their part in averting the danger.

SUSAN

“That’s the trouble of it,” said Trumpkin, “when most of the beasts have gone enemy and gone dumb, but there are still some of the other kind left. You never know, and you daren’t wait to see.” …

Lucy shuddered and nodded. When they had sat down she said: “Such a horrible idea has come into my head, Su.”  

“What’s that?”

“Wouldn’t it be dreadful if some day, in our own world, at home, men started going wild inside, like the animals here, and still looked like men, so that you’d never know which were which?”

 “We’ve got enough to bother about here and now in Narnia,” said the practical Susan, “without imagining things like that.” – from Chapter 9, “What Lucy Saw,” Prince Caspian

From this quote, being practical means focusing on the problem on hand. Susan didn’t want to worry about “imaginary” things – she only wanted to deal with those that are “here and now.” Perhaps that became her problem later on – when she got back to England, she only wanted to deal with the “here and now” and convinced herself that Narnia was only imaginary.

EUSTACE

“Why is it called Aslan’s table?” asked Lucy presently.

“It is set here by his bidding,” said the girl, “for those who come so far. Some call this island the World’s End, for though you can sail further, this is the beginning of the end.”

“But how does the food keep?” asked the practical Eustace.

“It is eaten, and renewed every day,” said the girl. “This you will see.” – from Chapter 13, “The Three Sleepers,” The Voyage of the Dawn Treader

From this quote, being practical means asking questions about things that don’t seem to add up logically. Eustace never lost this trait until The Last Battle, which adds charm to his character.

There is a positive and a negative side to being practical. As long as we make sure we’re not like Jadis, Uncle Andrew or Arsheesh, then being practical should be okay.