What if this were a thing in the games?

"what would the purpose be?"
Suppose it meant that a Pokemon would inherit it's evolved forms base stats. You could evolve your Charmander all the way to Charizard, but like Charmeleon most? De-evolve it for a Charmeleon with Charizard stats.

Could also open the door for new split evolutions. Evolve via de-evolution and re-evolution.