One of Comet Cache's most important tasks is ensuring that an outdated version of the site does not get served to visitors. If you change something on the WordPress Dashboard that affects the front-end of the site, Comet Cache will make sure that it clears the old version of any related cache files so that a new, updated version of the cache can be generated.

Comet Cache clears the cache in the most intelligent way possible. It does this by monitoring events in WordPress. There are some events that may trigger a clearing of the entire cache. These are considered "significant events" that affect many areas of a site and therefore Comet Cache has no choice but to clear the entire cache. Examples include changing WordPress settings, installing a plugin or a theme, and adding, editing, or deleting Categories and Tags.

What's so special about Categories and Tags?

Changes to Categories and Tags, which include adding, editing, and deleting actions, nearly always results many small changes to the front-end of the site. That means it's simply not possible for Comet Cache to know exactly which cached pages a Tag or Category name may appear.

For example, let's say that you renamed a tag called apple to banana. Now think of all the possible places on a website where the tag apple might appear: the home page (each post tagged apple might have the tag listed underneath it), the post itself (obviously), any Tag archive page that might mention the apple tag, any date-based archive pages that might have posts tagged apple... the list goes on. If Comet Cache does not clear the entire cache, there may be cached pages on the site that still refer to (now renamed) tag banana as apple, and therefore Comet Cache would be serving an outdated version of the cache to visitors.

The same is true with Categories.

There are so many places on the front-end of the site, so many places that may already be cached by Comet Cache, that need to be updated when you make changes to Categories and Tags. That's why the safest thing for Comet Cache to do is to clear the entire cache whenever a Category or Tag is changed in any way (created, modified, or deleted).

Why is the cache being cleared when I save a new Post as Draft?

Creating a new post and saving it as a Draft does not clear the cache, but creating a new post, and then creating a new Tag/Category and assigning it to the post, and then saving the post as a Draft will clear the entire cache (again, creating a new Category / Tag is one of those major events that if we don't clear the cache could result in an outdated version of the site being served to visitors).

Why is the cache cleared when I activate or deactivate a plugin?

Clearing the entire cache on activation/deactivation of a plugin occurs because Comet Cache has no way of knowing if the plugin being activated or deactivated is designed to change the output on the front-end of your site. If the plugin being activated or deactivated does affect the front-end of the site, then activating or deactivating that plugin would cause the entire cache to become outdated. For that reason, Comet Cache clears the entire cache to be safe.

See also: Disabling the 'Clear Cache' Routines on Plugin Activation/Deactivation

How can I disable the Automatic Clear / Wipe Cache Routines?

If you'd like to disable all of these automatic cache wiping routines and take full manual control of when to wipe the entire cache (using the "Clear Cache" button), they can do that using an MU-Plugin: