By default, the quest log does not preserve the "collapsed" state of quest categories. That is, when you click the "-" on a category header to get them out of the way, they are all shown again the next time you log in. Continuing my tradition of making changes so trivial that nobody else would think to code them, this addon stores those settings across game sessions. That's all. Nothing fancy.

Only the base API functions are used, so other quest log addons which also use the base API should magically have their collapsed categories saved and restored also. If they do the work themselves then you won't see a difference.