sqlcounter & reauthentication flag

Hi, I just heard about a so-called "reauthentication flag". Has this something to do with the sqlcounter-module? Could I use this flag to logout the clients automatically after their login expires instead of using the sqlcounter module (as I do not get a self-compiled fr running properly)? How would I have to use it, is there some documentation somewhere? If I use neither sqlcounter nor this flag, do I understand correct, that the clients would not be logged off automatically after their login expires? But they could not login again after expiration? Thanks for this hint, Jan