Although this is diverging a bit from the topic at hand, I've found that this dictates what I write - mainly string trio or quartet, since I know people that would be willing to play them, whereas I know fewer (competent) percussionists or (any) windists (I know there's a better term here but it escapes me at the moment).
Also, I compose. I don't play any instruments, and I'm not very good at composing (or maybe I'm just amazing but humble :whistling: ) but the point is, it feels presumptuous asking someone who has put in years of learning an instrument to play something by me, who has put in months of learning composition.