Real people have useless talents. What about your characters?
If a talent is truly useless plot-wise, do you even mention it in the story? Lets assume we're working with a novel, where there's more room for character development and backstory. Still, even in a novel, you don't want to ramble and risk boring or confusing your readers. How could you work a detail like this in appropriately? What would be the wrong way?
And then of course there is Chekhov's Gun. A character might have a talent that seems useless, or even a liability, until the climax. How do you pull that off believably? There might be some middle ground, too. Like, a talent that's useful a few times but doesn't come into play when beating the bad guy. That kind of detail can make a character seem more rounded, if you pull it off right.
This is kind of like two questions, unless you think about it as a question of balancing details. So sue me.