We have a lot of stories about feral cats and stray cats who find a loving home, which is great. If those stories inspire you to be good to the cats around you, that's great, too. If you've been making friends with a "stray" cat in your neighborhood, it's possible that the cat is abandoned, or it could be a feline con man, accepting food and scritches from anyone willing to give them even though he has a permanent home. Adopting a new cat would be a terrible mistake if that cat belongs to someone. Feral cats are easier to spot, as they are afraid of people and usually not all that healthy. But that cat that hangs around looking for human interaction may or may not be a stray.
On the other side, if your cat is on a diet and doesn't lose weight, he may be out there trying to convince your neighbors that he's homeless and hungry. My tomcats have made friends with all the neighbors and get treats from many of them. It's a good thing I've made friends with the neighbors, too. They aren't fooling anyone.