Downtime is very important for most people who work in offices and it's the recharge to our batteries that is needed for fueling us for the following week. It's not only important for the body but it's vital for the brain and the soul. Let's face it, once we retire we do get a lot of free time but it's in our older years and we shouldn't have to wait till those years for it. Everyone one should ideally work hard during the week, for 5 days and no more and get Saturday & Sunday for leisure. Or any two consecutive days off from work in the week.
My philosophy is that Monday-Friday you work and use the evening downtimes like after 7pm or 8pm for relaxing in between. Friday night starts the party mood and a few beers and dinner with your buddies isn't totally out of the picture. You should get Saturday free to do the things that you want to - go to the movies or shopping or completing your errands. Wanna travel to see your friends or relatives? Saturday is the best day to do so. Wanna hang out at the local cafe, go book shopping and buying cds/dvds? Great! Have a long lunch out, come back home for a little rest and then change to go out for a few round of drinks and dinner with your gang.
So you drag yourself home and manage to change into your jammies and collapse in bed. Sundays are for snoozing, relaxing in bed, sleeping in, cuddling with your wife, reading books, watching a movie or 3 from your bed and experimenting with new cooking recipes with your spouse. Perfect downtime and you are recharged for the next 5 days of work and the next Saturday.