People who keeps their computers on the ground will come across many problems. Gravity is your first enemy because it makes all the dust, animal hair, and dirt in the room end up on the floor which then gets sucked up into the computer. Frequent dusting inside your computer will be needed to keep it from getting too hot. Especially intel chips get slow if they get hot.
Whenever I see a box on the ground, it is usually covered in scuff marks because it ends up getting kicked. If the machine is turned on and the box is kicked, it can permanently damage your hard drives. Inside the drives there is an arm that carried the laser. It only locks into the bay when the unit is off. Especially when it is reading/writing, if it is jarred, the laser can scrape against the plates inside the drive and leave scrapes and scratches all over the drive. This usually results in hard drive failure. Hitting the machine out of anger will do the same thing.
If you are somewhere where there can be water, putting a computer on the floor is not a good idea.