Make your most loyal customers into owners. They are often your most passionate evangelists.

Investors have a financial interest in helping your business succeed. For instance, if you own brewery and your customer is also your investor, she'll likely drink more beer there, and bring her friends more often. 

Need help recruiting an an engineer?  Looking for an intro to a key VP at a big company?  Want feedback on your product from an industry insider? A crowd of investors can help increase your "luck surface area".