There is a few things to consider with the suspension. Spring tensioners, that's the little rings at the top of your shocks, the wt of your shock oil, and position of the shocks play a roll also. There isn't anything chiseled in stone so you just have to work with it a little bit and find out...
Pretty much self-explanatory my man, when the car comes down hard it bottoms out and the chassis hits the ground. That's chassis slap,
When your shock or suspension are too stiff, your car will be harder to control so a little chassis slap isn't bad at all.
That's were driver preference comes...