house cats can become "overweight" through lack of exercise and over-feeding because people don't watch them. when they get "spayed" or neutered ("fixed"), they tend to exercise less. spaying is done for queens, and neutering is done for toms. it is important to fix cats, and here are some reasons. first of all, if a female cat has kittens, they will need homes. finding homes for kittens is often quite difficult. if a tom is not fixed, it develops a disgusting smell. breeders who have entire toms keep them in a special hut outside the house, for that reason. fixing also helps to avoid over-population. over-population means that there are too many cats, and some will be put to sleep (put down) in animal pounds (animal shelters).