no no I cannot build then!! I need my leaf house pls
~ @buttfly29
Player placed leave blocks don't decay - via Leaves – Official Minecraft Wiki
I understand I can break them, but when I am just trying to gather wood, it is kind of nice not to have a Canopy of leaves still up, after I have harvested the wood. Sometimes I am lazy, and just don't want to spend time breaking leave blocks.
It also helps in keeping area's that you are logging free of Mobs when the sun rises up, where if the Canopy is still there, then Zombies and Skeleton's will stick around. Again sometimes lazy, and don't want to have to clear an area out of Mobs, just to continue logging.