The first example collapses all the layers into one, which can result in a smaller image than the second If a layer creates a file and then a subsequent layer

The first example collapses all the layers into one, which can result in a smaller image than the second If a layer creates a file and then a subsequent layer deletes it, the deleted file is still present in the image taking up space. If you squash the layers, the deleted file is gone “scratch” used to be an empty layer, but in newer versions is now just syntax to state that you want a layer without a parent layer