Does social media affect SEO?

Google says it does not affect search rankings & traffic. However, from my understanding it does affect. Users who come through social media can also be an organic user next time.

Also, a website with high audience on social media have a high chance to get promoted in SERP. These users also can be a word-of-moth publicity for your brand and hence, can bring more users in the form of search, social & direct traffic. When Google says they monitor the sentiment of a brand to calculate page rank, they can do it only by looking into its social profile (FB, twitter, Instagram etc.) to calculate the sentiments of a business. 

There are some other straight wins of Organic Traffic if you do your Social Well:

1. It helps us to index a page faster when you share it on social media sites.
2. Leverage local search results
3. It personalize the search results if you have a strong influence in social media
4. Gain authority in your business area.
5. All the shares on social will act as a back links (inbound links) to your website.