I've done that a few time actually.

My last company they flew me from another continent to do a 3-days assessment, I worked with the team on a legitimate feature(that would be trashed after as they couldn't use the code because I was unpaid). I liked it, I met the team, I interacted with them, I did the task and got a job offer in the end.

All engineers at the company highly valued the 3 days assessment because we got to select great people to work with, but we were getting too many candidates giving up or false negatives, they eventually cut it down to 1-day despite our protests.