Good topic...I swear, my opinions on this have gone back and forth for the past couple years.
I've definitely had 601+105 last (solid beeding) a rediculously long time. Through harsh north east winters with minimal "touchless-o-matic" rinse offs.
However, I don't think 601 does anything for the appearence of either 105 or 111. This is probably because I always run around the car with a PC and KAIO before applying LSP's.
IMO If you'll be using another cleaner/AIO/glaze type product before 601 and you're not shooting for super durability, it's really not needed.
But I'm convinced it adds to the durability...for now at least...my opinion will probably change again.