The current BT technology has not been able to hurt the hard disk, and usually read and write the hard disk, the damage is negligible. Just to protect the hard disk and the machine, don't keep downloading for several days in a row, and don't control the number of simultaneous downloads to more than 10 as well.
It's best not to do too much data manipulation when downloading, such as cutting and pasting files, so that the hard disk doesn't die of overwork.
The most crucial thing is not to have a sudden power outage when the hard disk is being read or written to.