For you, the benefits can extend beyond financial. An opportunity to engage with a small business broadens your base of experience and expands your network. This combination often leads to unenvisioned opportunities.
A good relationship starts with clear agreement and understanding by both parties. Be aware that many small businesses rely on getting gratis advice or support from their network. Define the boundaries of your relationship for scope, time, and money. Holding to these can be difficult as you get more heavily engaged, but it is important to do. Small business is inevitably personal, but you can ill afford to become emotionally engaged in multiple small businesses. This can present an opportunity, however, once in the door to expand a relationship and realize those "unenvisioned opportunities."
A common mindset coming from Corporate America is that you are either a full-time employee or unemployed. Engaging with small businesses in a consulting relationship can present an opportunity to test the waters before "jumping ship" or to create some income once in the water before engaging in a specific entrepreneurial venture full time. (Somehow that became a very wet analogy, but I'll stick with it.) The small business space creates a wide breadth of opportunities for those willing to look for them. As you have conversations in this space, I guarantee that you will begin to find them if you are aware of them.
A final comment. Realizing this opportunity is in your hands. Small business owners are rarely actively looking for this type of support. If you can point it out to them, assess the potential, and identify specific ways in which you can help, you can typically find a path. Be creative in finding ways to make it work, since small businesses are rarely rolling in excess cash for several hundred dollars an hour in consulting fees. In the end, it creates new opportunities for you and the small business.