> 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.