Someone turned down investing in our company. And I greatly appreciated it. I wasn't particularly excited about the answer itself, but the speed with which they said no was invaluable. It allowed me to quickly gather feedback, establish a friendly relationship, and move on.
The quick no seems slightly off-putting at first. Why hadn't this person taken the time to ask follow up questions? Research our market? Test our product? In reality, the quick no is infinitely better than the slow, researched, labored no. (In last place: maybe's and no-responses).
The beauty of the quick no is that it saves everyone time and actually preserves the relationship. The longer a tough decision is left unsettled, the more that decision hangs over your interactions with that person. A maybe or a slow response not only hurts the relationship, but frustrates and prevents at least one party from moving forward with another important decision.
Someone quickly and respectfully telling you "No, here's why.." is the second best answer you can receive (the first of course being a "yes"). It's really an amazing asset for both parties when hiring, raising money, or even trying to "grab a coffee."
If there was such a thing as business tool belt, I'd throw the "quick no" right alongside the trusty "write short emails" and "bcc."