sys_acl_levels_members

Could someone explained this table for me please.  On the 7.1 install, there are only five members.  There were a few more that I removed.  I am only seeing two entries in the table.  The only membership levels currently are the system levels.  All five members have standard accounts.  What should I see when examining the sys_acl_levels_members table?

It is rather important that I know about this table; how it works, what updates it.

That table is normally empty if all your members are standard members.

The only time something will appear in that table is if a member has switched themselves or been switched by admin to a different membership other than standard.

However, only deliberately setting a member back to standard will remove the member from this table. If the membership expired then the expired membership may still be listed in the table.

Thank you for your reply, it is appreciated.  I did a rather exhausted search on this, both on the forum, and using google, without finding anything that directly explained the table.