I have to agree with Mojo. A perfect example is people who pay monthly for their webspace and bandwidth. If I put a file on there and posted it in #mapcore then I'd be prepared for everyone in there to download it and whatever bandwidth loss that may result in, but I would not be happy if then about 4 people #mapcore then started spamming it in other channels, posting it on forums, on their blog sites and god knows what else without first mirroring it. My bandwidth would be used up and my host would literally cut my site off until the end of the month.
So yeah, when you start taking large links without permission you can actually start wasting people's money, which is why people tend to get a little pissed off about it. I personally just adopt a procedure of looking through my logs, and if somewhere is heavily leeching my bandwidth I'll replace the link in question with a gigantic goatse.cx picture or something. That usually stops them.