It would be really practical to controll hinges and rotators with the slider while building Wich makes checking for center of lift and mass easier. The sliders don't need to be physics simulated and should work in increments so that you can change if it should just snap at 15 degrees or 30 and for precision maybe even 1 degrees
Check out THIS suggestion and upvote if you like. I agree that this option would be great in designer mode. One workaround is rotating the rotator with the assembly using the rotation tool. It doesn't simulate movement but if does allow you to roughly see how the movement will look and will also allow you to see any shift the CoM.