The idea of less being more fits well into the theory of painting. The power, beauty, and strength of statement can be greater when the picture is stated simply and not overdone. Holding back is important in painting. Here's an anology. A legal document drawn up by laywers says everything there is to say about a subject in precise detail but most often will not convey much in the way of meaning to most people. The same is true of painting. Put in every detail and you'll loose the importance of the big statment...the very thing that attracted you to the subject in the first place only to get caught up in the smaller but less important details.
