I'm guessing this is the big reason why you don't consider it for your business, in the first place;
Buying new computers is so cheap to begin with, why bother?
So, let me start there with reason number one;
1. As much as prices have been lowered, you still have to consider how much computing power you actually need. Are you buying too much; beyond the needs of running your applications efficiently, by purchasing new equipment? It may be that a slighty older version is exactly what you need.
2. Refurbished computing equipment is also recycled computing equipment. It's a great way for your business to do its part for the environment. According to research from Gartner, 150 million "obsolete" computers are sitting in storage worldwide.
3. When you purchase refurbished gear, shop wisely. You can get the same warranty protections and service agreements on new gear.
4. Refurbished is not always "used". Again, shop around. Refurbished gear is often "discontinued" or returned gear never even taken out of the box.
5. Refurbished gear is a competitive market. There are generally two ways to go; you can buy directly from the manufacturer or through resellers. All of them want your business, so chances are you will save a significant amount of money even compared to those "rock bottom" prices on new gear.