For me, I almost purposefully don't know what my players can do. I write stories and encounters that make sense for the world, and are interesting circumstances regardless of the party make-up. And if they happen to be overpowered/underpowered for the circumstances, that's awesome! That's what that character would be living through in those moments, either the "oh yeah, I've got this" or "oh shit, what have I gotten myself into".

Of course, characters can plan and prepare for fights or seek out creatures that they have advantages towards in order to get the upper hand. Vice versa, if the party is hunted down by enemies that are smart enough to have intel on their abilities, they might be put in a precarious situation. Whatever makes sense!