Some time ago there was dismay on Mastodon (and Pleroma ?) instances about data scraping. Before that happened there were privacy concerned people automatically deleting their own toots, limiting them for example to the latest toots for thirty days. With Lemmy things are different since Lemmy is a link aggregator rather than micro blogging, and Mastodon has boost option (Called replay with Pleroma ?). However deleting your older comments (but not posts) automatically would be really nice for privacy reasons.
This is something I don’t like because I often forgot things about people I know and need to refresh my memory.
It is also my way to understand other people.
If you put something in public, unless it was an error (which should be deleted in a little period of time) I think that should be still there.