Before I left Reddit, I used a plugin through the api to replace all of my comments with random gibberish and then delete them. Part of this was because (mandatory) fuck spez. But more importantly, it was to protect the anonymity of my account. After years of posting, there is likely enough personal information shared to potentially connect my Reddit habits to my online identity. I wasn’t planning on using Reddit again in the future on that account, but I left it open in order to maintain some security control over the account. I’m not really sure what to do at this point because I still consider it a security vector that’s a bit concerning. There’s no way I can manually edit and delete all of my content with the snail’s-pace reddit UI, and I have no ability to assure that my content will remain unavailable or at least not publicly displayed.
If you’re storing change deltas rather than whole copies of comments, the changes for all of Reddit should be far smaller than the comments for all of Reddit.
Even storing full comments isn’t much more storage. Just consider it as another random comment from someone else. Doubt most people edit their comments so 95% of comments only have 1 copy. Hell they used (maybe still do) ignore edits in the first 5 min or something likely so people could fix typos/formatting before they start storing history separately.