When you feed other people's cat, the cat begins to like you more than its original owner. If you go on feeding it and the owner hasn't given permission, the cat may try to move in with you. This can make the owner worry about their cat and where it is.

Also please do not encourage cats to wander further than they should. They wander at their own pace and where they feel safe. If you encourage the cat to go further, then the cat may get hit by a car or may get lost. These are both rather unlikely as cats are very intelligent, independent creatures, but they may still happen.