TLDR: Assuming a fixed qr code size, more resiliency to noise (mud on image, etc) requires putting more information in the code. To fit this the boxes need to b

TLDR: Assuming a fixed qr code size, more resiliency to noise (mud on image, etc) requires putting more information in the code. To fit this the boxes need to be smaller, so that's harder to read. But if you're in a noisy environment and actually need the error correction it's still worth it.