Yes, most people stand back from a large print or painting to take in the overall artwork, but they very often then approach as closely as they can, to study the finer details. It’s a natural human behaviour to get close and seek out the details.Depends on the art. This triptych by Hieronymus Bosch deserves closer study than the 4.3 m / 14' viewing distance that your diagonal measure guideline would suggest is optimum.
People viewing the painting at the Museo del Prado in Madrid tend to stand much closer than 4 m.
As an aside, I should add the caveat that in museums and galleries people also tend to approach artworks closely simply because there are other folk blocking their view...
The *optimum* viewing distance for a photograph varies according to the size of the print, the level of detail “expected” to be seen, the subject matter, and the angle of view and camera-to-subject distance chosen by the photographer. A wide-angle landscape for example is usually best appreciated from a very short viewing distance, which helps to recreate the immersive experience felt by the photographer surrounded by nature’s glory.