Why? Steam and pressure will cause your tile to come unbonded from the subsurface, whether it be concrete slab or backer board. When the pressurized steam breaks that bond, held together by the thinset, between the back of the tile and the subfloor, your tiles will give off a hollow sound when you walk on them. If you drop something heavy enough on a hollow tile it will more than likely break and could send the shock wave to surrounding tiles. This then becomes an expensive fix that was caused by improper cleaning techniques.