As he wanders around, he may meet other cats. Often times, cats who do not know each other will fight, and they can really hurt themselves. Some neighborhood cats never visit the veterinarian and may have cat diseases. They can make a roaming housecat very sick if he plays with them. Probably the greatest danger to a wandering cat, though, is traffic.
Neutered cats are less likely to stray far from home.
This means that they get very loud and call out.