The advantage of a B&M for e-juice is the ability to taste test, and even occasionally buy small bottles to see how it steeps (I have tried a couple that were fine in the store, but after steeping tasted medicinal or just nasty). But usually once I know for certain I love a flavor, I look for a better price and larger quantities online. Literally just got 30ml bottles of one of my favorites online for half the price of a 15ml at my store.
As for APVs/Mods etc., in a similar way, I do like to check them out in person before considering a purchase, check local prices, then dig around online. 9/10 times bats, chargers, tanks, accessories etc. will be dramatically more expensive at a B&M, plus most do not keep a wide variety in stock.
My personal preference right now is APV, I have tried out one of the vape shop guy's personal RDA's and it is pretty sweet of course, but I am usually too buy with work and school to refill or rewick so often. And I prefer something a little lighter weight when I am driving as well.