Any ceramic wall tile over 12” should be installed with at least 1/8” grout joint and a 33% offset. The 4x16 ceramic tile pictured below is staggered at 50% instead of 33%. This tile has a little bow in it (which is normal), and it tends to show when it’s installed close together and the lighting is close to the walls. Avoiding a 50% offset will ensure that you are not installing the tiles highest and lowest point next to each other, which is what causes this installation to look bowed.
Make sure that the light is at least 2 FEET away from any wall to prevent this shadowing effect. This can be difficult when you have a light inside the shower.
Under-mounted cabinet lighting should be pushed as far away from the wall as possible to avoid highlighting slight bows and imperfect grout joints.