i was trying to remove the diff fill plug by using my foot to torque the wrench, but it unscrewed so fast that the wrench hit the ridges of the diff housing and cracked some pieces off. should this be of any concern? why are the ridges there in the first place?

 

Ridges are there to dissipate heat. If one or 2 are cracked or broken its not a big deal.

 

but check to make sure that the cracks dont go deeper into the housing