"What is the purpose of level 39 & 40?"

#PokemonGO: Upon reaching level 38, you can power up your mon 1 final time before the button disappears.Thus... what is the practical purpose of trying to level up to 39 or 40? It won't affect your maxed out mon at all via /r/TheSilphRoad http://ift.tt/2izIYWD