I think there're two main reasons or applications for connections with high bandwith: p2p and VoIP. I agree with HoreTore that if p2p would be declared illegal and suppressed by ISP's then a lot of people would cancel their contract and go for a cheaper line. Even though VoIP is on the rise, p2p is still the main traffic on the web.
What I don't get is Husar's point that when I actually use the connection as I pay for (600K/bit flatrate) it is bad for the ISP's. There's no restriction on the amount of data I can transmit. If it would be a problem for the ISP's when everybody used his connection to max then they would be wrong to sell the connections. If they have to expand their carrier net, they need to do that. They have to anyway, unless we want to stop the internet evolution right now. I'm aware that in some countries the Internet is still sold by the Mbyte or GB but if I buy a flatrate I want a flatrate, meaning no restrictions on volume of data.
Imagine for example I wanted to help spread linux distros by torrent. I could run my torrent client with max upload 24/7 and not break any points of the contract.
there's only so much bandwidth between backbones as well and expanding them costs an ISP money that they will hardly get back from their customers who pay exactly the same whether they download a lot or nothing which is why I mentioned flatrates
I think the ISP's are making enough money from people who don't use their bandwidth to full extend because they pay exactly the same whether they download or not.

BTW, cutting a DSL connection every 24 hours is completely normal and has nothing to do with the bandwidth you're using.