This addon remembers collapsed groups in the faction window and restores these settings when you login the next time. It is useful for me because I was tired of always scrolling down the whole list to check my WotLK reputation standings.
The addon is very small and zero config. So just install and be happy.
Sidenote: In the current version the addon minimizes the number of times your collapsed groups are saved. To be more detailed, this only happens when the faction window is closed (or changed to another tab). So for the very unlikely case in which you open the faction window and log out without closing it, changes to your collapsed groups will not be saved.