It's not a question of "critical" modules. It's a problem that can occur if many different signals are sent to a single input, all of them set at 0 dB. Lowering them may help, but better signal path design is the real solution.
There are no real rules regarding the knobs, just places where one fits beter than the other. When you have Hz, Milliseconds, levels in dB, real measure units, the KNOB will work better as it can be quantized to any of those reference units. When something is measured from -1 to 1, or from 0 to 1, a PERCENTKNOB comes very handy as you have the range covered in 0 to 100% control.
Modules control inputs understand numbers sent to them If a module has a range of -100 (dB) to 0 (dB) the PERCENT knob sending out 0 to 100 means nothing to that module. Math should be correctly used and applied in relationship to the mosules inner parameters values and ranges. More math can be done using other modules to conver a parameter to a percentage but this requires extra work outside of the modules you have used so far…..
It's such a powerful place….