I know someone..
Who smokes an extremely large amount of pot every day. Like.. a lot. I smoke occasionally on the weekends, and I've had him over - he smokes so much pot, you can't see in the room anymore, and he's still nearly sober. He smokes up, then goes to work. In roofing and carpentry. He works 12 hour days high, and does a better job then anyone else I've known. It's fucking insane.
On the flip side, I know another, older lady, who has really bad arthritis (who was an alcoholic, but can't drink because of the meds) who smokes a very large amount every day, and is basically a lay around vegetable.
It's all in moderation, or body chemistry. I choose to moderate, just like people who might have a drink on fridays after work. I tend to lay on my couch, eat some chips, and watch movies or play video games. On monday, I get up for work and school with no problems.
Oh, and my depression? Had it for years, don't really have it anymore after I started smoking. Because I can have that day to zone out at the end of the week and recharge, not stress, etc.