Agree with everything above, that it is easier and creates a better angle.
That said, it can be dangerous to do a true pivot too often, and personally I still encourage any southpaw to step off rather than pivot 95% of the time. A good pressure fighter that sees you like to pivot should be struggling to hide a chubby. If he can dictate the timing and placement of your pivots, he is in a very strong position to land his left hook, and catch you stepping into it, which lets face it, can often be a fight changing shot.
For example, you will likely try and pivot when a swarming orthodox pressure fighter shifts his weight to his right side, as that gives you the most range, time and opportunity to capitalise on the change of angle. If a swarming pressure fighter, seeing you like to pivot, steps right and hangs his left hook out as he does it, it is unavoidably going to find its way behind your guard. If the guy can punch, that one shot alone could be enough to spoil your evening. At the very least, it will give him a golden opportunity to land a few more game changing shots when you are off balance.
As for out maneuvering him, one move I like when fighting a pressure fighter who comes swarming forward is to be in your orthodox defensive stance, step back into a southpaw stance, and then step immediately back into the orthodox stance. Pressure fighters always seem to get confused by this, either over committing or under committing, which either leaves them lined up for some hard straight shots they weren’t expecting, or gives you the space to step off and catch them adjusting.