What and why: At our Confluence site we use WEBSEC_CONFLUENCE_USERS as the general group for users, since this is a requirement of our User Directory (LDAP). If a user logs in and creates his personal space, the other users still don't have access, even if he checks the "[x] registered users" question at personal space creation time.

At personal space creation the question appears...

Choose who can view and comment on content:
[x] Me
[x] Registered users - anyone logged into Confluence

But who is "registered users"? It's the standard group "confluence-users" that is entered into his space permissions to read and/or write.

So the improvement would be: The Confluence Admin should be allowed to set which group is meant by "registered users".