If anyone's fitting 4-pot calipers for looks, well, fair enough.
If you're fitting them thinking they work better, that you somehow get better braking and/or better fade resistance you really need to ask someone other than the salesman who is selling them to you.
Its a matter of piston area. The more the piston area the more force is applied to the pad for a given amount of brake line pressure. This is why performance bikes fit 4 and 6 piston calipers, because they don't have power assistance, so the amount of braking you get is limited by the strength of your hands, so their benefit is increased piston area. Race cars fit them for a quite different reason. You have really sticky tyres so you want a lot of pad area to get enough friction to use all the grip you've got on the road. To do that with a single pair of pistons they'd have to be huge, so you use multiple pairs of pistons to create a caliper that's compact so you can fit as big a disk as possible.
Its not the 4-pot caliper that improves fade resistance. Its the size of the disk. The mass and its ability to pump air through it to get rid of heat. A 4-pot caliper is longer and thinner so lets you fit a bigger diameter disk inside any given size wheel. So if the road car has power assistance and isn't running a bigger disk its really hard to see the point.
