Years ago, I had machines all over the room. There were atleast 3 of them in my tiny little room... Wires all over. Back then I used to keep the cases off all of them 'cuz their hardware was being swapped like crazy. Never had a problem leaving it open... except once I closed it without looking & a real live mouse had gotten in, & got decapitated by the fan... I noticed the stink 2 days later & removed the case & almost puked...