However, as the story progressed, this character was more often troublesome than helpful. I kept having to remember he existed and thinking that he should be in the scene, or have more to do.
If I had to keep reminding myself that character existed, how important was he to the main plot? Yet if I cut him out, all that material I'd already written would have to go.
Also in that character's favor: My hero would very likely have such a character in his employ. On the other hand, given other elements of my hero's background, I could offer a valid explanation for that lack.
I liked the guy. He had some good lines, too, lines that won't work in any other character's dialogue. You can't just take lines from one character and put them in another's mouth, not unless you intend to change the latter character's personality, so they'd be gone, too.
I had a vague notion he could eventually become the hero of a sequel. But I had no clear ideas for specific story for him yet.
So despite the points in his favor, I made the tough decision to take him out of the story. Now I have to delete all references to him, all his dialogue, all his activity, all reactions to him. This is not particularly easy, nor is it enjoyable, but by taking him out, I'll have a tighter story with more emphasis on the main characters.
This is the sort of decision that makes writing difficult, even painful at times. But it's also part of what separates writing from typing.