A hearty laugh gives one a dry cleaning, while a good cry is a wet wash. We all have our own unique constructs and beliefs and opinions about play and fun and joy and laughter. I lump play, fun, joy together to capture a feeling distinct from laughter. Physiologically, laughter introduces oxygen into the body in a way that few other actions can.
Laughter also exercises inner muscles that are otherwise hard to exercise.
Healing on the physical, emotional, mental, and spiritual levels are often attributed to the act of laughing. For laughter to be effective, the content or stimulus is irrelevant. I have friends I laugh with about things that are not funny to anyone but us. We laugh with tee-hees and guffaws and belly laughs. It's deeply healing.