Updated: Apr 9, 2019
Play, by definition, is fun. When play stops being fun it stops being play.
During play, pups exercise their bodies and minds, making them healthier and smarter for it.
Domestic dogs seem to be endearingly suspended in a juvenile frame of mind. Thus play is not something they outgrow but rather an activity they keenly pursue throughout their lives.
play serves as a barometer of well being, indicating that a dog is well fed, in good health, and content. Dogs, like humans, do not play when they're sad or distressed.
Dogs that do not seem to enjoy playing should be carefully scrutinized to make sure all is well in their lives.