There is nothing illegal or wrong with using torrent clients, so long as you're not downloading or "sharing" copyrighted material. I use utorrent 24/7 to seed linux distros and other free and open source software, as it's a good alternative to direct downloads for people who have limited internet speed or want to download large files. If you're paying for a certain bandwidth, you have the right to use as much of it as you want. I would recommend saving and seeding torrents on a separate HDD from your OS, or at the very least, on a separate partition. And to answer your question constant use of utorrent or whatever other torrent client you use will shorten the life of your HDD significantly, in proportion to you internet connection speed
