Its so much harder to cut off a person from circling when in an octagon. 8 sides, and the angles are so wide it is almost like a circle. If the fighter doesn't have good footwork, he is gonna be chasing his opponent for the entire fight.
Gives an advantage to fighters who circle and counter punch though. Fighters like Bisping, Machida and Anderson Silva, the octagon benefits them.
Anderson Silva ♔
Aldo - Dos Anjos - Mayday - Weidman - Machida - Jones