The only improvisation I’ve done with other musicians was when I was in my high school jazz ensemble/various jazz combos I gigged with for awhile. I think it’s a really important skill to have as a musician in any style, being able to think on your feet and knowing your instrument well enough to be able to play whatever pops into your head.
But improvisation is actually kind of an integral part in creating my own music as well. Quite often I’ll have some sort of foundation laid down (beat, chord progression, etc.) without knowing exactly what I want to happen on top of it. So I’ll just hit record and start improvising melodies. Sometimes I come up with an idea I like but needs work, so I’ll develop it further. But sometimes that initial improvisation makes it to the final version of the track.