I pay for software, but I won’t pay for software if I’m not sure I’ll use it. MacHeist has allowed me to purchase software that I was curious about, but that I wouldn’t normally buy, because I wouldn’t use them enough to justify the cost. Previous examples are Pixelmator and VectorDesigner; current examples are Acorn and Espresso.
I don’t know how much the developers got from my purchase, but it is more than they would have had otherwise. I don’t know how much they would be willing to pay me to refer them to a friend who was switching to the platform, but they got that too.
So what MacHeist has done is allowed me to pay developers to market for them in return for using their software which I wouldn’t have used (or purchased) otherwise.