Funny - I just went through an app re-org Saturday (when I was on a wifi-less flight) and did all of these things.
Usage-based icon arrangement: This group organizes app icons based on the frequency of the app’s use.
Relatedness-based icon arrangement: This group (which I find myself in, incidentally) organizes apps into cluster based on functionality. If you have a screen of photo apps, for example, this would be you.
Usability-based icon arrangement: Some people organize their apps so they can reach the ones they need most often with their thumb, without having to swipe too much or accidentally click on other icons.
Aesthetic-based icon arrangement: These people organize icons in ways that are pleasing to them. For example, they might keep their first screen sparse in order to see the background image of their girlfriend, or they organize icons by color or patterns.
External concepts for icon arrangement: Others report using systems imposed on them by external forces. For instance, their icons are arranged by order of download, or they keep the icons in the default arrangement pattern suggested by the hardware maker. One user organized his icons alphabetically. (via The Five Ways Users Organize Their Apps And What App Designers Can Learn From This | TechCrunch)