We've had our pool for one year. Installed and closed right away last year. From what I've read, it all depends on where you live. In places where you will have frozen water you want to be below the lines to make sure there is no water in the pipes and that when it freezes (ice expands) it won't creep into the lines. It can be pretty expensive to fix what ice breaks.
We are in MN so will definitely drain 6" below the skimmer, disconnect and drain all hoses, the pump and filter. We may add RV antifreeze just as a precaution. Will also be placing a cover over the filter to help protect it from the elements and probably bring the pump inside (probably unnecessary but we've got the space so better safe than sorry).
This of course is after we have gotten every single leaf and pine needle out of the pool, brought it to shock level, given it a good vaccumm and placed the winter cover on it.