The purpose of o-ring lube is... wait for it... to lubricate! Without lubrication, as you tighten the seal the o-ring can bunch up and deform, which could either leave you with a leak, or cause the o-ring to fail sooner, and
then leak. The lube allows the ring to maintain its shape while you tighten.
Regarding the debris, while it's true that debris could cause a seal failure,
the solution is not to avoid lube. You clean all three surfaces carefully (the ring and the two surfaces that it will touch), with a lint-free cloth. And then clean your fingers, too! Apply a
light coat of the lube to the ring, and then assemble.
Try to avoid a couple things:
1) assembling your o-ring seal in a sand storm, and
2) talking to pool store employees!
