Luminous Landscape have a great article by Alain Briot about choosing a print size that suits your subject matter, and how print size can in turn influence what you take photos of.

“However, many decide on print size for practical reasons rather than artistic reasons.  Some print at the maximum print size of their printer.  Others print only letter size.  Many print most, if not all, of their work in the same size.  This situation is very common, and if you feel that I described your approach, do not take it as a critique.  Take it as an opportunity to learn a different approach, an opportunity to try something new that has a significant potential to improve the artistic content of your work.  You may also have very good reasons to print your work in a single size and no desire to change.  This is a situation that is not only understandable, but which has been taken by some of the finest photographers.  Again, my goal here is to present alternate possibilities as well as reflect upon a specific aspect of landscape photography.”

Website: Luminous Landscape - Subject Matter & Print Size