Yes the brain releases doses of serotonin, also there are psychological benefits such as an improved self-image. I quit working in offices and changed over to physical and outdoor careers over four years ago... it was the best thing I ever did for myself. I found this hugely improved my attitude in general over the years. Mind you I still get down, but nothing like when I worked office jobs under florescent lights all the time, and got no physical activity other than typing on a keyboard. There's certainly something to be said for a hard days labor. I would strongly suggest anybody that is in an office work out at least once a week.
When I was in college I had a very busy schedule, but I could always find an hour in the evening to speed walk/jog a few blocks. I liked night jogging because the local park was always empty. I don't like public gyms... two reasons... I don't like people watching me and there are always those nosy people that are rude and stare, the other would be people sweating all over equipment and leaving dirty towels, used band-aids etc... groooossss... so I bought a bunch of free weights, a bench, and a skipping rope to use in my basement. I find working out six days a week with 60% of your maximum weight to absolute exhaustion is good for building muscle... get 3000 calories at least though or else you won't gain much. Otherwise, if you want to keep tone and fit, three times a week with primarily cardio exercises work fine... but I find that everybody has to find what's best for them. I have an unnatural metabolism, so I burn weight waaaay to fast... I need to eat a lot, do heavy lifting, and do only minimal cardio or I lose all muscle tone.
Oh just to mention, when I was too poor to afford equipment, I would use whatever heavy objects were at my disposal for weights instead... full paint cans, pails filled with water, tire rims, etc... plus push-up, crunches, and jogging cost nothing. So no excuses... and, unless you are completely paralyzed, then any disabilities you have should not be an excuse... my cousin always says cause he messed up his shoulder that he won't play any sports for fun, or go workout. Just because he can't lift his left arm above his shoulder shouldn't exclude him from keeping fit or joining in on sports... its just an excuse for some other reason that he just doesn't want to share.