It's so that you can have a change in the stiffness and or suppleness of your hook-length.
Rigs can be made using mono which is either stiff or soft, there are several theories on using stiff and soft through the hook length to help hooking; so various monos were joined together, then someone came up with the idea of coating braid so that you can peel back the stiff coating to leave the supple braid.
i assumed it was so when the carp goes to suck up the bait it flies in easily, and I suppose on ejection, either through normal filtering of detritus or because of detection of resistance, line stiffness doesn't effect the outcome.
Except for D.A.M. Quick all the major manufacturers have made inferior quality reels for the cheap market; I've never seen a bad Quick reel. I have Shimano xte-a 10000 and rate them excellent. Since they're discontinued you have to sniff them out second-hand.