I'm going to differ (a bit).

There are certain images that need to be large, because of their content, and their intended audience.

As an example from the world of painting, I refer you to the painting "Las Meninas", by Diego Velázquez. This is 318 × 276 cm (125.2 × 108.7 in) and in real life is absolutely stunning. It would not be as powerful if it was smaller.

Here is a link: http://en.wikipedia.org/wiki/File:La...ogle_Earth.jpg

So I would say that the size of the photograph depends on the photograph, and where and how it is to be displayed.