A vasectomy is a surgical division or resection of all or part of the vas deferens usually to induce sterility. Vasectomies are helpful to the environment because they control the population by restricting the number of children in your family. Also, my wife no longer has to take birth control pills (less demand for plastic containers, one less monthly trip to the pharmacist). An additional benefit is that my wife doesn't have to take her pharmaceutical on a daily basis and she is spared all of the side effects that go along with it. Also, if I get divorced, I can't start a second family and treat them better than the kids in the first family.
Unrestrained population growth adds significant stress to the environment. China has had success in curbing the growth in its population, but their policy of one child per family is too harsh. I believe that voluntary population control (along with tax incentives) is a sensible approach. A voluntary vasectomy is one way of achieving this aim on a personal level.