Just to clarify the spin attack isn't just a different animation, it attacks in a 2 square radius around your character. To put this into perspective a normal melee attack only hits at a range of 1 tile and only in the direction you are facing.

The spin attack can hit people who are diagonal/ multiple people at once, and because of the extended attack radius it makes it really good for attacking people who are trying to run away, or to get some free hits on people trying to melee you who aren't looking in your direction.

If it was just an animation that didn't do anything it would have been part of the default attack