Prompted on kickstarter for info for getting stuff. A required item for the response is my phone number.
Q: "Why do you need my telephone number?"
A: "It was one of the basic questions when we made the surveys. I guess we might need it for tracking info and shipping? If it is a problem, just dump a 555 number or something. We are never going to call you or anything."
If your response is "I guess...?" then you didn't think hard enough about the form.