Very much liked this article from the Ceramic Tile Education Foundation. Much useful information including the excerpt below.
Evaluate the Finished Installation from a Normal Distance
Perhaps the most important aspect for evaluating a finished installation is the viewing distance. It should be viewed for acceptability from a normal viewing distance, not a foot away or closer.
Normal viewing distance assumes that the viewing is done without a magnifying glass or microscope. The idea is to experience the completed project as users of the space would.
It also assumes normal lighting.