Grout is a necessary and integral part of many tile jobs for several reasons.
Tile floor no spacing.
Where the tile is being installed.
It follows that the maximum height of the arch will be midpoint of the tile or in your case at the 12 point of the long 24 edge.
12 by 24 tiles can have some bow to them instead of being perfectly flat when set on the floor they ll have a slight arch.
As a general rule floor tiles should have grout lines of 1 8 inch or larger depending on the type and size of tile.
It is not recommended to go below 2mm for wall tiles and 3mm for floor tiles due to the requirement of stress relief.
The instructions for installing this tile state using tile spacers speaks of the grout lines suggested size being 3 16 so i would triple check to be certain that these are a self spacing tile as i see no where that that is listed as being the case on any site.
Where you are installing your tile should also be considered when choosing your grout size.
Crater lake 3x12 design.
It keeps moisture out of the substrate helps keep tile lines straight and.
How to lay tile without grout lines.
Special types such as slate or quarry tiles often do not have edges uniform enough to look good with tight spacing.