Members with 4 wheel disc systems: Can you lock your wheels?

Might mention that on the cable show (since retired) Fantomworks, a test they did on every car was to see if all 4 tires left skid marks. They didn't go further and judge the front-rear bias. I've heard for that, such as adjusting a rear proportioning valve (aftermarket w/ knob), you set so the fronts skid just slightly before the rears skid, in a wet parking lot, though never done that (have such valve on 2 cars, but not driving them).