[quitit]

The difference between the Apple “precomposed” and standard icons had to do with the gloss effect on icons on pre iOS 7 home screens.

When adding a website/webapp to these earlier home screens, the OS would apply a gloss effect over the icon in order to match the aesthetic of the standard apps. The precomposed icon was a way for the developer to stop the OS from applying this effect, such as if their logo already had a different gloss effect already applied (i.e “precomposed”) or other design where adding the glossy shine wouldn’t look right. The standard icon allowed the OS to apply the gloss effect - which was a timesaver as Apple did tweak the gloss contour over the years: hence using a standard icon ensured that the website/webapp always matched the user’s OS version.