The main ones for me are

It's got on boarding and de-duplication, on PieFed if I view eg. this post https://piefed.social/post/749818#comment_6102866

It combines/aggregates it with cross-posts/reposts

So I can see it in one place, and see all the comments in one place.

Subjectively speaking, after switching to Piefed I feel like "the internet is back".

Engaging conversation, good tools for filtering the front page to your liking, and the audience seems generally speaking more mature. I do expect that to change if the platform grows in size.