The main reason to do that is to make it so that you don't have to redownload everything if you have to fresh install
Or to save space on a limited OS drive.
I personally download then all to my SSD for faster install, then occasionally move download files to HDD.
But I don't download much so I have no concerns about the extra writes to my ssd
But including all you guys mentioned, isn't it recommended to change download location from main SSD with OS installed in it to other less important HDD in order to protect against drive corruption from virus?