If a dog is wagging his tail, they won't bite you. A wagging tail must be interpreted in context with the rest of its body language. Sometimes when a person smiles, it means pain or nervousness. Likewise, sometimes a wagging tail is not attached to a happy dog. A dog should go through a season before being spayed.
Any heat cycle carries risks, of uterine infection or unwanted pregnancy.
It also increases the risk of mammary cancer later in life. Taking in more calories than one burns off results in obesity, whether you are a dog or a human. Most mature dogs and cats are overweight to some degree- obesity is probably the most common health problem for our pets, too. It is easy to blame a surgery for overfeeding. If a dog scoots on his rear, he has worms.