Dedicated web hosting is expensive and shared web hosting does not enable a client to enjoy benefits as dedicated hosting does. VPS hosting is a mid way between the two, providing the best of both the world: exclusiveness of the former and low cost of the latter.
Virtual Private Server hosting has become very popular for it provides the customers the facility of hosting their site on an exclusively private server, irrespective of the other websites on the same server. It is as if the client owns the server individually and can configure it as per his own needs and requirements to the extent of customized rebooting.
A lot of companies providing hosting services have started providing specialized VPS hosting services to their clients as it also relieves them of the need to monitor the server and leave it to the client to administer the server capabilities on his own.