One of my favorite experiences was that as an intern I shipped what I thought was a useful tool. When I came back full time a year later it had spread and was pretty popular among a subset of the company!

My interns always got very speculative projects, the kind that were low probability of working out so didnt want to waste (more valuable) time exploring. If they ever found anything useful it was 100% reworked from scratch.

My preference was for both sides to learn at the end of the day.