I believe the 125 is a 6' tank. In a tank with that dimension you can have small tangs easily. Also for working, on a corner tank, you generally have just the back against the wall. With the corner tank, you have two sides against the wall. So there is easier access.
Finally, there is the sump. On a rectangular tank, you can access the sump from both ends and from two doors in the front. But in the corner tank, only the front.