beacuse a per-click program evens out fluctuations in your per-sign up revenue, if you ain't big in traffic.
It's reassuring to have a fairly steady income. As for the sign-up programs, some weeks can be really shitty. If I had 50K worth of traffic to play with, instead of 15K, the law of great numbers would see to it that my sign-up programs returned a steady cash flow with only small fluctuations. So it's really a statistical concern...
