It's not that the weight or wing loading of big models becomes less important. It is VERY important. It's just that the best all around wing loading for larger models is higher than small ones. It is still just as easy to build a BIG heavy pig as a small heavy pig. The key is knowing what a good wing loading for the size and type of model you are doing is. As daRock said already this valuation is based on subjective experience by hosts of model builders of that sort and size of model that preceeded your efforts. It pays to research their results.