The dangers of torrents are the same as any other type of download, really. The advantage is that it's a pretty nifty way of sharing a file amongst many people. Basically, all the people connected to each other share random parts of a file (or set of files). Helps save the bandwidth of those with the original file, and makes it more likely the end user will be able to complete the download even if there aren't any others with the full download currently on.