Neutering cats makes them less likely to spray and mark territory. Spaying eliminates her heat cycle. Females in heat can cry incessantly and show nervous behavior. Females in heat attract unwanted male animals. Pets are less likely to bite.
Pets are less likely to roam, run away, or get into fights.
Spaying and neutering does not make an animal fat or lazy. Too much food and not enough exercise is the main cause of obesity. It is actually better to have her spayed before she goes into heat or has a litter. Also, for every one you place, another animal is being killed someplace else because a home could not be found. Neutering does not remove the guard dog instincts.