It has been suggested that play is a necessary part of growing up for all young social animals and that without it they may not develop to their full potential. This does not appear to be the case, as animals deprived of play for reasons of sickness or ill health grow up to be behaviorally indistinguishable from their play-satiated peers. This is not to say that "players" may not develop more rapidly than their play-deprived peers, just that the end result often turns out to be more or less the same.
If play is not absolutely imperative for normal development to develop, what good is it? Well, play is a role-playing rehearsal for adult behaviors and as such will prepare a youngster for what lies ahead. During play, pups exercise their bodies and minds, making them healthier and smarter for it. In nature, this may give players the edge over their unrehearsed counterparts who may be still struggling to learn the Ps and Qs of canine etiquette or the rudiments of the chase. Note that different types of play unfold in parallel with sensitive periods of learning, so that play learning is most efficient. Mouthiness is first seen at 3 weeks of age, right after the transitional period. Then come play solicitation, play fighting, scruff holding, deference, and finally sexual play.
All these forms of play start in the socialization period between 3 and 6 weeks of age and they intensify as the pup approaches adolescence. Object play, chewing and chasing objects, occurs a little later, becoming most intense after about 16 to 20 weeks of age.
