Kitchen tiles should be thick – heavy items dropped on a thin tile may break the tile. Twice the thickness typically equals four times the strength. Thinner tiles must be fully bedded with no voids under the tile…or they will definitely break upon impact.
During installation, working a tile (pushing it down) into the bedding forces the adhesive to rise up the joint space. Using for example a 6mm thin tile will leave only a mm or two for epoxy grout to protect the adhesive from chemical attack. Metz recommend a minimum 12mm thick tile be used for commercial kitchens. Metz can also offer 15mm and 20mm thick tiles.