Yeah I don't know why the OP is getting flak for this, it's a great trick!
And obviously, the biggest reason to do it is organization and ergonomics. I think SONAR will eventually integrate buses and tracks in the Track View, it just makes things easier. Then we could take that Shift-B bus pane and make it a custom area where we can put whatever tracks we want. In fact, we can have tabs of them for quickly jumping to custom groups. AND we can still have our buses in the Track View arranged however we want.
This gets even better when you use multiple gain stages or split sub-groups out for things like parallel compression. I've many times ended up with VOX-SUB buses that then feed into a VOX-MAIN bus after some weirdo routing.
And yes, why NOT allow routing audio from a track into another track? Sure we can bounce down but that takes us out of the zone and now we have to go new track hunting and moving it to folders etc etc. If we could just insert a track and quickly render some experiments or subs we could move faster. Not to mention whatever weirdo things we might be able to do with it. Sheesh someone using Ableton figured out how to make a wobble by chaining a billion things together and now there's a whole dang sub-genre of electronic music from it! (dubstep in case you were wondering).