I do the same on Reddit and similar sites (including HN), though I never delete any comments, just the accounts. I've become increasingly uneasy about leaving a digital trail, especially as there are increasingly advanced techniques to correlate accounts via stylometry.

For Reddit specifically, if I needed to, I would look up old comments in Pushshift if I could remember enough information to locate them - keywords, approximate date, subreddit, username. It's somewhat annoying that this service no longer exists. Though there are dumps, and backups of those dumps, so hopefully someone will release a similar search tool for these, eventually. Perhaps also including the data scraped by Archive Team. Maybe I'll have a crack at it myself as a side project.