If you are at the stage with your business where you're far too busy and all your time is spent doing tasks you don't want to do,  a VA can help lift some of the pressure and allow you to spend your time where you really need to (ie, on growing your business and focusing on the bigger picture). You can hand over all those jobs that you don't really have time for or simply don't want to do.
Hiring a VA gives you more time to grow your business, without the commitment of hiring an employee. You only pay for the hours you actually need, plus you only pay for time spent working on your business (no paying someone to take breaks, check their phone or finish early on a Friday!).