We've been told for years that file size doesn't necessarily mean higher quality, though it's usually regarding megapixel counts on camera sensors. But did you know that there's a point in Photoshop where increasing the quality setting — and file size — actually decreases the image quality? That point is 7.
When saving JPEG files, Photoshop uses chroma subsampling — which hacks off colour data because your brain doesn't register it at the same rate as brightness — up to 6. But after that it saves all colour information. To keep the file size progression linear, rather than having a humongous size bump moving from 6 to 7, files are more heavily compressed at the 7 setting than they are at 6. See? Less really is more, except when it's less, or when more is also more. [ImpulseAdventure via PetaPixel]