Some don't even request/want you to send your step scores.
Others specifically request to see them.
I would assume the ones who want the scores are definitely looking at them, though I don't know where the importance would rank (vs. other factors). I would think it would matter if you did remarkably bad (like low 200's or less) or remarkably good (i.e. 250 or more) but maybe not so much if you are anywhere in between.
I think only one of the interviews I went to the PD mentioned something about us being there because of our "good personal qualities, excellent academic achieverments, including research and high USMLE scores" or something like that. It never came up in the vast majority of my interviews, though.
If you have particularly good step scores, you might want to preferentially apply to more programs that request you to send the step scores, and if you have lower step scores, might want to prefer programs that don't ask you to send them.