In general, there are more submission options from open guard and more more sweep options while in butterfly guard, but it depends largely on how you train. Most people train regular guard more, so they are better at it but also their opponents are better at defending attacks from guard.
I think Rich Franklin uses a Butterfly guard if im not mistaken...
He used a butterfly against Evan Tanner, who has an uncanny ability at getting a full mount on his opponents. The butterfly guard negated Tanner's attempts.
I think that The butterfly guard throws off OPP like switching sides when mounting top in wrestling.. its just differnt and some guys dont know what to do with it..
the butterfly guard allows you to control your opponents hips and conrol were they move easier but the closed guard stops pretty much any offense the opponent has. to go for any sub attempts your gonna have to open your guard sometime.