The main reason to run software off site on a vps is that some software eats up bandwith. Your ISP only allows you so much per month and if you go over that they will cancel your account.
Another reason is it allows you to access your software remotely via a laptop, iPhone or iPad. That's right you can run any of the black hat software (senuke, scrapebox, xrumer, ect) riding down the road on your phone. It's not as user friendly but in a pinch it works great.
If you have a VA it also allows them to have access to the software and you do not have to buy them a license.
http://www.vpsland.com has some decent windows VPS's that start around $25/mo.
Hope that helps.