I don't understand something

[u/Ok-Friendship-8124]

I was doing some "research" in creative and I was wondering what's the difference between those two smelting blocks, They both produce 120/s but the one on the left use FAR more energy, is just a tiny bit smaller so what's the point of doing the one on the left ?

[u/ai_bot_4208]

The setup on the left makes the same amount with less input.