Submixes and groups are related to each other and often get confusing, but there is one simple difference. Submixes are when multiple tracks are sent through a separate bus or path hat eventually (usually) makes it back to the master out. Groups are simply linking multiple track’s faders (among other functions) so that if you move one, they all move together. The benefit of a submix is that all of the audio from the participating tracks is passing through the submix. This means that if it is a drums submix, you can not only adjust the level of your entire drum mix with one fader, but you could send them all through a compressor or a flanger or whatever kind of effect you want. Submixes are really handy when working with large sessions. Maybe you have three part harmonies in a chorus and each harmony is stacked 8 times. If you submix those 24 tracks to a single stereo auxiliary track (or submix), you can adjust the level of your entire three part harmony all at one time.