Well... there are extremists everywhere. The moisture left in the cart would cause flavor loss, lower nic str, and less juice to be able to fit in there. I personally don't think it's much of a difference myself, but for some, those reasons could be enough to want to completely dry their cartos out.
The mg str can be a big deal to people if they think they are losing some.. My father in law vapes 24mg and is convinced 18mg isn't enough.. I mixed up a bottle of juice for him that was 18mg, and labeled it 24mg, and he's been very happily vaping away for a couple days on it and haven't had any nic cravings like he did when he knew he was on 18mg. I'm tempted to mix him up a batch of 9mg and see if labeling it 24mg will do the same.
