Tile can be placed on the floor if you want it. The major precaution is to make sure the floor can support the weight. A single tile may not be that heavy, but when you add the weight of (potentially) hundreds of tiles it really adds up fast. Also, make sure the floor surface doesn't have any "bounce" to it. If the floor flexes in any way, it will lead to cracked tiles as they try to flex with the floor.
Tile can be placed on the floor if you want it. The major precaution is to make sure the floor can support the weight. A single tile may not be that heavy, but when you add the weight of (potentially) hundreds of tiles it really adds up fast. Also, make sure the floor surface doesn't have any "bounce" to it. If the floor flexes in any way, it will lead to cracked tiles as they try to flex with the floor.