Here are the other five factors that largely determine the best resolution for a print.
The viewing conditions affect the resolution needed.
If your mural-sized print of the Grand Canyon is being displayed in the brilliantly-lighted visitor center of the park, then a higher resolution is needed.
If the same mural-sized print is used in a dimly-lighted restaurant in Topeka, a lower resolution will be sufficient.
This is because the cone cells in the eyes, which perceive color, also are responsible for visual acuity.
When the light is low, the cone cells don't function as well, reducing perception of detail.
If you print a photograph, at the same resolution, on different paper surfaces, the resolution will appear to vary.
Gloss and semi-gloss papers will show more resolution, while matte and watercolor papers will show less.
Consider the subject matter of your photograph when deciding which resolution to use.
A foggy seascape may need far less resolution than a close-up a lobster.
Because the smaller sensors of point-and-shoot cameras have greater noise, this may be a factor when deciding how much resolution is needed for a certain size print.
This factor may be insignificant.
The human eye is far more sensitive to brightness than it is to color.
Therefore, the resolution may have to be higher for a B&W photograph versus a color version of the same photograph.
A color photograph, in which brightness levels are prominent, may need more resolution than a color photograph in which brightness is less of a factor.