Often, it is easier. However, the differences between species are sometimes more subtle and we have to look at parts of the tree we don't usually pay much attention to.
Key features are bark, twigs, and buds.
However, other features are sometimes important, such as branching patterns, overall form, habitat, and taste. Once in awhile we can use leaves on the ground or brown leaves that still remain on the tree. Working these keys takes practice. Carefully compare the descriptions with your sample and your memory of what the tree and habitat looked like. It is best to use a mature tree, or one that is not a seedling or sapling.