My homepage is cached (in the page cache), but does not ever stayed cached for more than a minute or so. It is because I have the default options set in the Purge Policy, which includes purging the homepage cache "when posts are created, edited, or comments posted".
I'm not creating or editing posts at all, but I am getting 1 or 2 spam comments every minute or so on my site. These spam comments cause my homepage to be purged and regenerated.
It would be a great benefit to not have the homepage (or any page) be purged if a spam comment is received, as opposed to a posted, or pending comment (we actually moderate all of our comments due to too much spam, so any "good" comment goes straight to pending status).
I'm not sure what hooks are available to the w3tc plugin, so maybe it's not possible to know if the comment is a "good" comment (as opposed to just any comment) at the time w3tc does its check to purge the cache, but I think this would be a great improvement for performance. Instead of invalidating our homepage every other minute, we'd have a long lived homepage in our cache (since we only get a handful of valid comments a day)...
Thanks for your help. Great plugin!.