@DrQuinn I definitely see them as RP hooks and also a visual presentation of character development. Both for other readers and the player of that character. I saw in another post that someone mentioned that some players treat these games partly as a CRPG that is closest to a TTRPG and I can definitely see that. When I play a character, I try to create one or pick a roster character that is more of a blank slate and let the character shape itself through the adventures and scenes they participate in.
In my opinion, vignettes can definitely help both for the player to write out how they see their character growing in the story they are part of, but also let others in on it as well. Vignettes also play a part in plot +requests the player puts in, being able to show what may have happened with dice rolls that happened behind closed doors.