Hello dear Donncha,
I am using wp-super-cache on one of my blogs where I do not post often (www.r-statistics.com).
In it, I set the expiration date of the cache to "0" (meaning, if I got it right - keep them forever). But I also said to clear the cache I publish a post or clear it if a comment is added.
However, I have just got a comment held for moderation. The comment was spam and I marked it as spam. But when I went to view the caching of the site, I noticed that the homepage (and the post on which the comment was submitted) had their cache refreshed.
Shouldn't it be that the cache refreshes only when a comment is posted (not marked as spam)? Or did the cache clear because I was an admin or something of this sort? (I also looked at the cache from incognito mode from chrome)