Robert,
Good tutorial. I would like to add to it though. One of the best uses for bus mixing is as a sub mix for say, backing vocals, drums or orchestra. I know that most of us don't record a drum set but I'm sure some do and maybe multiple tracks of backing vocals as well. If you set the output of all your drum/Bvox tracks to a bus and then route the bus output to the main out, you will be able to change the level of the entire group of tracks with one fader and retain your mix instead of having to move all of the seperate faders at the same time. If you have say, five tracks of you singing backup for yourself all mixed well with each other then you can now adjust your backup vocals in relation to the overall song mix without the danger of changing the sub mix of bvox.
Also, I believe that GT3 is set up so that your aux channels are effectively sub busses but I may be wrong on that count. Regardless, your advice is sound and, as has been noted earlier in the thread, you can get a clearer definition between tracks using your technique. As a side note, I don't claim to be a pro by any streach so judge my advice by my products, you may choose to ignore my ramblings after a few bars. Cheers.