Merge vs Replace clarification

The best answer to this question was brief: "Merge creates a folder with all items from both places." To my mind, it helps to imagine a collection of pictures, say of "holidays" and you have a backup you want to keep current. If you add photos to the active version and at the same time decide to delete some poor pictures, then Replace is what you want to put in the backup. Because Merge will find the ones you deleted in the prior backup, keep them in the merge and defeat your intentions. This helped me understand it.