I have chosen pitted travertine/marble tiles, 4x4, for a kitchen backsplash. The tiles are cut such that they fit together perfectly, and because the surface is slightly "pillowed", the effect of no grout with the tiles placed side to side is absolutely stunning. My installer had me lay out a 3x6 foot test section, and when he viewed how well they fit edge to edge, he said he would be willing to install without grout. Is there any reason that grout SHOULD or MUST Be used? I definitely do not want it unless I absolutely have to. Thanks.

In a backsplash if the tiles are not getting wet and you like the no grout look, go with no grout. If the area has a chance to be getting constantly wet, then you need to grout to protect the adhesion of the tile to the wall.