CloudFlare® enables you to use full page caching using their servers that is served on their CDN. The only way to use remove page from cache is by using their API.
Purge Cache for CloudFlare Plus and its parent plugin use that API to remove pages from CloudFlare cache when some actions happen. For example, when post is published, it sends request to CloudFlare to remove cache of that post, home page, various related taxonomy, archive, parent, child, sibling pages.
There are several most common actions covered and for each of them several most common related pages are removed from cache. Plugin takes care of API limits, sets proper headers, has priority list of pages that should be purged, sets pages that shouldn’t be cached.
Other than this, plugin also provides easy user interface that change a few settings it uses.
The difference from the free parent plugin is that there is more coverage of purged pages (free only purges basic ones) and that there is user interface for settings so you don’t need to use filters for that.