Tolkeen posted a thread about it that was largely ignored
End corner combos in u4 and you're at enough advantage to whiff a sc immediately after it. You can bait wakeup attacks to punish your sc and then punish them for full combo. Very gimmicky
The only legitimate use for it I have found is when you win with kenshi and it's time to fatality, use his sweep to pimpwalk up to your opponent, then finish them with an u4.