depends on what you mean by "having fun." play is important. it's how we learn. it strengthens bonds between humans and helps us develop social skills, coping skills, etc. even as adults play is important. i go out and ride my mountain bike, which is fun. to me it's play. for some it's getting a "workout" and exercising, getting healthy, etc.
going out and getting stupid drunk is "fun" but is it worthwhile? if you need to blow off steam and de-stress, yeah, i think it's worthwhile. all depends on how you look at it. to me, "having fun" is worthwhile, you can't always be "serious" and stoic. i think you should "have fun" no matter what you are doing, no matter how important or serious the task, you can "have fun" with it.
i agree with prothero up there. having fun might be the only thing worthwhile.