Suppose I want to rout all my vocal tacks through a compressor and reverb, would I use an Insert Assignable Fx for that or a Bus with the Fx added to it?
Assignable Fx is very similar to an aux send / return set-up on audio mixers and consoles. For instance sending vocals to a rack mount reverb. The 'return' typically does not contain the dry signal.. just the reverb.
"I don't get the "The 'return' typically does not contain the dry signal.. just the reverb" > The reverb is blended in the with the dry signal that is already in the mix
"What if I set my VST reverb to 50% wet, then it already contains 50% dry as well." > You could do that but there's no point in the reverb Fx scenario.
"Are suggesting only putting the reverb at 100% wet on the assignable FX and playing with the return volume to control wetness/dryness?" > Yes, the reverb plugin's parameters are typically set to 100% reverb and the dry signal setting is muted or set to infinity (off). You will not be arrested if you do otherwise though.
"What about the Bus? how does that work?" > The 'FX Bus' is the Return which 'contains' the plug-in. When assignable FX is inserted, the aux Send fader is added to the track headers, just under the volume fader. Like most pro consoles, the aux send can be set to pre or post fader. It could also be used for a mix minus scenario or to create an alternate headphone mix for the players.