[singingboyo]

My thought is that signaling before the full check gives the other driver a chance to make sure they're comfortable with and prepared for the change, but obviously you want to know they're there already.

I think the missing point in that SMOG acronym is general awareness. I don't know if they teach this, but I won't signal unless I'm already quite sure I'm lined up with a clear space I want to get into. But, once I'm aligned and think I'm good, I'll signal, double check mirrors, shoulder check, and then go. The only new info that gives is the shoulder check, and if you're paying attention a shoulder check should never surprise you.

If you need to change lanes within the next 30 seconds, and don't already have general knowledge of the destination lane's status, you've screwed up already. [1] It makes much more sense to consider checking after signaling if it's a double-check, not your first look at what's around you.