Are Social Media sites useful for Business?

Yes, they are. They help in optimizing the brand which makes it reach a wider range of audience across different platforms and countries with minimum effort and cost. Moreover, social media sites are more precise in reaching the targeted audience, as they help filtering users according to their interests and make it way easier to be reached.

It all depends on the type of business. Non-profits benefit a lot from social media sites like Facebook. Smaller, local businesses might benefit from other sites like Yelp,

Some businesses , social media won't help at all (in my experience, dry cleaners).

For online businesses, social media is huge for growth.