Hi.

Whenever an object is published all your cache-blocks will be expired, if you don't use ignore_content_expiry parameter. In this case, you will have to delete your caches manually or wait until expiry time will happen.

In some sites it could be nice to have the ability of expiry those cache-blocks only when objects of certain classes are published.

I'm thinking about sites where there's a lot of interaction with the visitors. (making comments, posting in forums and so on). Normally, if you think about your main menu as a list of 'folders', it wouldn't be necessary to expiry your cache-block for main menu whenever a comment is added.