Water softener cartidge?

I just received my "Total Filter Kit" and I am using the water softener cartridge. The instructions say to empty the remaining water from the cartridge when the wash is complete. Does anyone know how critical this is? It seems that I neglected to read the instructions until about two weeks after the first wash.

Also where I have the cartridge mounted gets full sun for about half of the day. Does anyone know if the sun heating the now dry resin will be detrimental to it?

Thanks