Is is beneficial to hire a virtual assistant?

A virtual assistant is usually less costlier than a full time assistant. I am an entrepreneur and I don’t have an assistant. I get my business letters written by my web content writers. They write my sales letters, cover letters, replies, mailers, online newsletters and other correspondence. They charge as per the actual work done and not by the hour as virtual assistants do. Their website is: http://www.freelancewritingdesk.com. Although i do not use virtual assistants, I have heard that the concept iis catching on and that they do a good job.