Originally Posted by Osiris
There are some fighters who specialize in X-guard (Marcello Garcia for instance). Its a great way to sweep someone whether its gi or no gi since you can get under your opponent just like half guard, but have more control over him and therefore have more options for sweeps and submissions.
Its not quite as popular as say your regular spider guard, but its a recently popularized position-
I find Butterfly guard to be a great way to get back to your feet in MMA. If you look at the Sudo - Royler fight, Sudo's defenses of Royler's sweeps and leglock attempts gave Royler some great chances to get back to his feet or go for leg takedowns - he just didn't, because Sudo is a superior striker and wrestler, so it wasn't a viable tactic to him.
If you watch the second Franklin - Tanner fight, when Tanner knocks Franklin down in the first round, his use of the butterly guard to nullify Tanner's GnP and regain his feet is picture perfect.
I just re-watched that fight and you're right, that was some beautiful use of the butterfly guard by Franklin that I never noticed before, he didn't take a single punch while he was on the bottom. (btw, that's in the 2nd round, when Tanner takes Franklin down with a single leg, not the 1st round knockdown)