Left hook is my go-to punch and I have a tendency to spam it without rhyme or reason, so I just wanted something to go after it and I don't have a very good short cross so the uppercut just made sense to me. Though, to me it flows about as well as its opposite...
As for benefits, sometimes the middle will open up when people are worrying about hooks, and most people expect a cross after a hook so the uppercut can sneak in there unexpectedly.
I'll have to consider trying it, I used to be addicted to the Lead Hook as well. Didn't really matter if it made sence to throw it or not, I just did.