Doesn't that squash all your layers though? That defeats the whole purpose of there being layers. Now instead of a huge total size, but pushing only a fraction

Doesn't that squash all your layers though? That defeats the whole purpose of there being layers. Now instead of a huge total size, but pushing only a fraction of it, your total is lower but you're pushing all of it every time. Same goes for disk space if you're running multiple instances or many images with shared lineage.