>I wondered, “Who is this feature even for? Who will use it?” No one on my team knew.

I think there's another key here - Don't assume someone else knows something. If you don't know why something is done some way, find out who does and make sure they do. I've been in so many situations where the organization gets complex - person A is loaned over here or person B is working on project X because team Y needed feature Z. So frequently you'll find out that core assumptions have been made because everyone involved was only half-involved and either kind of assumed someone else was taking care of it, or (more frequently) knows the assumption is wrong but is choosing not to say so for political reasons.