What benefits are there to partnering with other small businesses?

One of my favorite ways to create business is by partnering with others. I have partnered with a metal worker to create custom awards for the professional extreme sports fields where he did all the sales. I have two woodworker partners at present: one who creates for my business, and one where he does all the selling of his product with my lasering services. His clients have also become my clients, using me for products and services outside of my partner’s product line. When I refer to partners here, I am not talking about a business partner from a traditional point of view. We each have our own separate businesses and there are no contracts needed.