I hate this, but the fact is that small business depend on that. Facebook almost took over the web for most of my friend circle. they spend their lives there and have difficulty in finding stuff when it's not showing up in facebook search.
And google does not help in some cases, try searching for a product information. the first page is mostly shopping garbage.
For mainstream businesses, like chain supermarket, Coca Cola and car makers, I still maintain it's wasted effort.
I'm working at one of top digital advertising agencies in EU. National and global brands save no buck on their spending on social media presence, and there are plenty of cheap (for them) tricks that result in both additional sales, positive PR and new customers. We also have strong data to back this up and justify our budgets.
Sometimes it costs real peanuts. Its easy to pump sales for soda brand by going to Snapchat with staged clip going "PEOPLE!!! I WANT TO SEE HOW THIS SODA HELPS YOU BEAR WITH CURRENT HEATS!!!" with people in 13-30 range flocking back with clips of them demoing how soda helps them out stay cool. Then brand gifts dozen or two best submissions and next action ran month or two later attracts 120% the number previous one did, word of gifts and possible response from social media make sure of that.
Whats in for, say, Lidl (large market store in EU), when it gives away stuff to guy who complained to them on twitter that he got diarrhea from expired pizza he bought at their place? It lets them save face, improve recognition of their brand and makes more people bring their feedback, allowing them find potential rotten apples within their chain.
For young peopple especially the fact that large brand @'s them on twitter/face/insta or elsewhere is enough to go nuts, go to store, buy crazy amount of brand's product and then stage some photo or clip alone or with friends. And then there are followers who mimic this in hopes of getting social fame as well.
A few questions on the Snapchat thing, if you don't mind: Aren't you just "buying" interaction with the prospect of a potential price? Does it actually increase sales figures significantly, long term and beyond the people that participated? Wouldn't the participant have been very likely to buy the product anyway? I mean they already follow the brand on Snapchat.
Social media is simply new channel in BTL and is important to Brands as they grow the awareness that there's increasing number of people that's simply oblivious to ATL.
As for sales figures, we actually work within targets, sometimes esoteric ones like "get hastag trending on specific day". We also rarely work alone, more often than not being just part of bigger picture happening simultanously. Brand then reviews performance using market research companies or sales figures and tell us results, so its hard to say if sales change would be same or different without us.
As for long term sales, that depends more on Brand's strategy and its reception by the market. Digital is part of this strategy's realisation, but due to nature of the medium, we are playing short game here.
Not to mention you have a bad experience at a mom and pop and post about it on twitter, it WILL get resolved if the owner has even the slightest amount of sense.