Things to do według GoodDayToDie
Changing file associations, even ones that are supposed to be locked to built-in apps (like .MP3).
Custom system components (replace or modify the keyboard or Start screen).
Port Win32 programs, even ones that require drivers such as openvpn.
Change the default search engine.
Make the ringtone volume controllable separately from the system volume.
Toggle services on and off with one tap.
Enable raw network sockets (support other protocols than TCP and UDP, do security testing from my phone, etc.)