These settings let you control the cookie domain and cookie path of the cookies that b2evolution will set (especially the session cookie) when a user browses this collection.

You should normally not change this, except if you are using multiple domains or complex paths and you want users to be able to log in on a parent domain or parent path. But, again, the best way to do this is to configure b2evolution’s Baseurl as the highest level URL that is a parent to all the other ones.

For example, if you want www.yoursite.com, blog1.yousite.com and blog2.yousite.com to share the same cookies (and sessions), you should probably set your baseurl to http://yoursite.com/.