A very under utilised technique in MMA. Not because you can generate great knockout power, because in most cases you can't, but because it's a great way to close distance, and distract your opponent. It can also be used to 'drag' an opponents guard down if you can throw it well enough.
Firstly, using it to close distance and distract is a great way to potentially pull your opponents focus away from your hands. Following the technique up with a punch combination can be devastating (Mark Weir-Eugene Jackson)*.
Secondly, using the technique to 'drag' your opponents guard down then following up with a punch combination can be equally devastating.
*Weir's hook kick was not thrown with great technique, but was still effective.