Next you may start to see added switching. This is way cool. Go a little higher and you might even see a Mute switch next to every auxiliary send pot. Now, this is beyond cool. Here the design intent grows beyond function to improving sound quality.
Circuit design is approached differently.
Much higher grade components are used, and the layout may become more critical. If your budget has lasted this far, you might start seeing VCA subgroups. Let's imagine that you want to control all of the vocal mics with one submaster fader. With a standard submaster, the combined audio signal from all of those channels assigned to that submaster would flow through that submaster fader. From a functional standpoint, that's a bit of a limitation because the audio going through the individual channel faders is still there, even though you've dropped them from the house mix by pulling down the submaster.