I used to do both...thinking I was maximizing everything I could and having the perfect tool to shear the ink. I've done it 3 different ways.
1. Keeping pressure the same all around and using the mechanical up/down to control print pressure
2. Changing squeegee pressure and mechanical up/down
3. Cranking squeegees all the way so they go down as far as they can but using the regulator to control squeegee pressure.
Number 3 works the best in my opinion. It is much easier to use the right print pressure and not a pound more if you don't want to. I spent way too much time moving those blades up and down when it really wasn't doing anything. If you didn't have the blade down quite far enough you might think you didn't have enough pressure so you crank up the psi then you realize you need to move the blade down and forget to take some psi out of the cylinder and before you know it, your settings are all screwed up and you're not operating at your best. I know some would say what the hell does it really matter? Who cares or whatever but you already have to spend the time setting the job up and it doesn't take any more time to set the job up right than it does to do it wrong, so do it right the first time and move on.
Luckily I've never ran a press that didn't have squeegee regulators and I wouldn't run a press that didn't. I think it is a very important feature/option to have on an automatic.