1. a lot of doctors say no. a lot of women say yes. the 2 factors that can cause weight gain are water retention and increased appetite from either the estrogen or progestin
2. Well first of all there is only one day a month you can get pregnant. It is men who are fertile any time

Its just a matter of knowing when that one day is (by charting fertility signs) and then accounting for the 5 days sperm can live. But anyways... the way the pill works is to prevent ovulation, thicken the cervical mucus so sperm can't get through it, and change the endometrial lining so that if you have breakthrough ovulation a fertilized egg can't implant in the uterus.
3. Many women use it to skip their periods. There aren't any long term studies on safety but the FDA thinks its safe since they've approved Seasonale.
4. I haven't noticed any reduction in cramps.