My neighbour would smoke £100 of it a week if not more, was borrowing more off his dealer etc than he could pay for. He tried intimidating me and my mum to give him money for weed and when we refused he got violent and extremely aggressive. This is a man in his 60's... so personally, I don't think it's as harmless as some think. He was a horrible man anyway but a helluva lot worse when he couldn't get any weed.
That's my experience of some people who are smoking it daily. They smoke it all up when they get paid, so they need to tick some weed to tie them over, then when they're paid the last thing they want to do is hand over money when they want their weed so they then owe money. I've had to pay a friend out of debt from weed before because the dealer was in town waiting for him.
Also the people I knew who smoked weed tend to go on to deal it to help pay for their own weed and they've been so desperate they've tried to rob people for it or been robbed themselves when selling it.
Not saying by the way every single person who smokes weed is bad, can't handle it or a drug dealer, but certainly there's issues I agree.