When creating a Merkle tree, why is sortPairs set to true?

I watched the video, Building an NFT Airdrop, and Hadrien mentioned that {sortPairs: true} allows the proof to be more succinct. He said it had something to do with not needing to know the side that a hash is on. I don't quite grasp what this means. I couldn't find any explanations in the merkletreejs library and haven't had any success tracking down an answer via google. Could you point me toward a reference that would explain how this works? I want to make sure I understand this before using Merkle trees.

Great video, by the way! The OZ Merkle tree contract will make my project much more efficient.