It makes the expander ball slip out of the case neck easier than dry.
It's faster than q-tip lubing the inside of the necks and you can prime and load without case lube stickiness in the neck, that has to be cleaned before loading.
Lightly lube the bottom two third of the case with case lube and lightly dip the neck, size it.
The little Neck lube bottle is easy to knock over so I silicone glued it to a metal peanut butter lid.
