If you intend to use your gallery as a portfolio to get work in the field of graphic design, then tightening it up to hold just what you consider your best work might hold some merit, but if you are a hobbyist, it can be used to show how far you have progressed. Believe it's a personal matter... until recently I hardly posted anything, so my gallery size wasn't a concern, but now as it increases, may do some weeding, but not yet....