It is important for hosting companies to have a presence on social media as a large percentage of their customers will use social media services on a daily basis.
Social media is not an ideal platform for providing support to customers on regular hosting related problems, however it can be incredibly useful. For example, when a hosting company's server goes offline due to technical difficulties or a DDoS attack, companies can keep their customers updated using a service such as Twitter or Facebook.
Social media is an important part of maintaining a good reputation online too as it is where customers turn to leave good and bad feedback about your service to their followers. If you provide good service and great customer support, a customer may share the experience online. However, if you provide bad service and poor customer support, they will turn to social media to complain about you.
It is therefore important that you monitor your company's brand on services such as Twitter and Facebook so that you can share positive feedback with your own followers, respond to pre-sale questions, and check whether any negative feedback is being published.
My own recommendation is to create a social media profile for Twitter and Facebook. Larger hosting companies may want to consider using more social media services to connect to customers, but be aware that this takes up more time and energy.
The best rule of thumb to follow is to not create a profile for any social media service you cannot update and monitor on a regular basis since failing to respond to messages through a platform may suggest a company with poor customer support.
Social media support can be considered part support and part marketing. If done right, social media can generate a lot of business for you. If done wrong, it could end up losing you customers.