Mandatory Fun at Work...is it worth it?

Mandatory fun- a day that the boss (CO) sets aside for "morale boosting" events, such
as a barbque. And everyone HAVE to attend.
These days usually are at the end of the work week and geared toward rewarding the crew with down time. I spend more than enuff time with the people I work wit, I don't really want to hang with them when I don't have to. Then you really can't unwind. You be to focused on keeping the boss impressed or wondering if you are saying the right thing. The worst part of the whole thing is once you get back to work you have a desk full of crap to handle.
So what purpose does this really serve. I have to stay at work late trying to make up all the assignments that went unfinished during "mando fun"! Now I just wish the boss notice this. What are your views? Are you for or against "mandatory fun" and why?