I've been mining various cryptos for years now, sometimes with much sketchier equipment than hard drives (i.e. GPUs, ASICs), and these are my rules of thumb:
If a mining setup runs for 12 hours with no issues, while I'm around to check on it, it's good for 24/7 mining.
Anything that passes that last rule can be left on 24/7 and while I'm not home.
Mining equipment has to be located in areas that pets can't get to without supervision. (I don't have kids, but I imagine the same rule would apply.)
I shut the mining equipment down if I'm going on vacation or won't be home overnight for some reason.
Never say never, but I've haven't had a disaster yet while following those rules.