Springs holding exhaust systems together came from the race track.
If a pipe was damaged or a header has to come off in a hurry, un-clip the springs and it's off.
The transition to road pipes was like a lot of Race Track technology, it was "cool", "I've got a RACE pipe on my bike/car etc"
Bob is well know for building max power, so for him to specify springs to hold everything together is in line with that performance style.
(Just my opinion of coarse)
Personally, I don't like this set up on a road machine as over time the joints will wear as the springs do allow movement, this in turn will cause leaks.
I prefer to weld every thing together so there are no joints anywhere in the system.
It all requires a lot more precision of coarse, but that's not difficult.
Interestingly, I would never weld a Muffler to a header pipe, as it will always break !
Besides breakage, if you were unfortunate to drop the bike and flatten the muffler, as a separate component you can then just replace the muffler.