I have yet to figure out what a user gains if, since I'm not deleting their posts, I delete their account
I suspect that most forum owners--who, I assume, administer a forum more as a hobby or for enjoyment rather than as a career--would be better served by deleting posts of users that request that their account to be deleted. Yes, in the case of a member with tens of thousands of posts, this would be a problem. But such users also have a large enough investment in your online community that account deletion requests from them are
least likely. In fact, in my 11 years of admining, I can recall only one account/content deletion request from a user that actually mattered. I did not delete his content, and he didn't cause any resulting trouble.
By far, though, the majority of these requests come from users who have posted very little or have posted things of little value to the core purpose of your site. These same users can also often be the least pleasant to deal with--and yes, potentially litigious, as well--probably at least in part because they are in some state of irritation, having expended emotional energy on your site and been disappointed enough to want to erase any evidence of their having been there. So for you, the admin, the choice comes down to this: Do you want to stand your ground on the issue of not deleting content and deal with the worry that ensues from a user's expression of disgust, threat of litigation, or actual litigation? Or do you want to suck it up, delete the content, and move on?
@Anthony Parsons is correct when he says that most site owners "aren't as protected globally as they think when running a website."
Personally, I use
this add-on to get rid of a user's content.