@Morphoice The PMA outputs a modulation value like this:
PMA Output Mod Value == param(Value) * param(Mul) + param(Add).
It's useful when you want to control how much of a value you want to apply to something (among other things...)
IIRC now you can have more than 16 parameters in a network, but yes you could have your synth in a network and the filter in another. It makes sense.