I use keg lube on every keg when filled, but a teeny tiny amount run around the lid o-ring between thumb and finger - just so the rubber glistens. If the lid won't seal at ~15psi, then I add a little more, if necessary initially sealing the keg with high pressure. Of course certain kegs among my collection are more problematic.
I use it a little more heavily to seal dip tube o-rings.
I normally keep the kegs at 20-30 psi for the first three days, after which reducing pressure normally doesn't cause the same leak I got at low pressure/low lube.
When washing the keg, after soaking in hot PBW or PLC upside down in a bucket, I try to remember to run a wet, soapy sponge or paper towel under the rim of the keg opening to wipe away any residue which is negligible.
I personally don't feel that keg lube when used very sparingly is much of an issue when cleaning kegs. But when I run out (or maybe before then) I plan to buy CIP Film keg lube since it washes off more easily with hot water than LubriFilm keg lube.