My rule of thumb is simple: if it has frosting it stays otherwise it gets trimmed off. How you trim is dependent upon the strain and other factors. Tight nugs get a different trim than airy buds, strains with a lot of frosting on the leaves get a different trim than those with hardly any frosting. I have a plant where the leaves are absolutely covered with trichs, These I trim loosely, leaving much of the leaves. I have other strains that you don't see hardly any trichs on the leaves, these get a very close trim.