Suppose I'm creating a category tree with several levels, call them L1, L2, L3, L4.
My inclination is to put products within the leaf node of each path through the tree. Where most of my products have 3 categories they would be in L3 categories, some in L4 categories.
Is there any reason I'd want to also put the products in the L1 and L2 categories? For search or any other reason? Are there themes that expect a product to reside in all categories down to the leaf?