Source:
http://windows.microsoft.com/en-us/windows-8/what-appdata-folder

What is the AppData folder?

Applies to Windows 8.1, Windows RT 8.1

The AppData folder contains app settings, files, and data specific to the apps on your PC. The folder is hidden by default in File Explorer, and has three hidden sub-folders: Local, LocalLow, and Roaming.

Roaming. This folder (%appdata%) contains data that can move with your user profile from PC to PC—like when you’re on a domain—because this data has the ability to sync with a server. For example, if you sign in to a different PC on a domain, your web browser favorites or bookmarks will be available.

Local. This folder (%localappdata%) contains data that can't move with your user profile. This data is typically specific to a PC or too large to sync with a server. For example, web browsers usually store their temporary files here.

LocalLow. This folder (%appdata%/…/locallow) contains data that can't move, but also has a lower level of access. For example, if you're running a web browser in a protected or safe mode, the app will only be able access data from the LocalLow folder.

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