As long as your Mac is running, your internal HDD is being read and written, no matter what you're running. As far as torrent files, it depends on how you've configured your torrent app. Some have a selection for temp files and a separate selection for torrents that are completed. If you make both of those point to the external HDD, no torrent files will download to your internal HDD. Either way, it's just storage, so if space isn't an issue, you can download to your internal drive. Be sure to stay away from pirated software, as they can contain malware.Will using external hard drive for torrent have any effect on the HDD inside your mac (life cycle)? i.e. will your internal HDD be writing and reading before storing onto Ext HDD or is it only your extHDD that is going to be used. Or should I use separate trash pc as a sacrifice to download all torrents, and then transfer separately to mac to keep my mac in mint condition?