To use an old phrase, I work hard and I party hard. I massively enjoy both aspects of my life, and whenever it gets "out of balance" (not enough working or not enough fun) I begin to feel bad. Everyone has their own balance to find, but I agree it's really important to experience both ends of that scale to work out where your own middle is. I've worked 9am - 3am before, which was too much work, and I took 6 months off work before starting at my current position, which was too little work.