One of the most enjoyable things of being a developer is that you can quickly make stuff work together.
Getting to know other tinkerers is a great experience. It helps get new ideas, blow off steam and show off new tricks. Apart from all that it's important to share food and drinks with like-minded people. Combine all this into an early exit from work, followed by an evening of hacking, eating and drinking with other makers. Would be awesome, right? So why not join the next time?