Originally Posted by Thurallor
Just curious, what does making custom userdatas allow you to do?
Well, in layman's terms, it allows you to create an OOP system. In Lua, most types of data are forms of userdatas; that is, file handles and similar. You can check the type of something using the 'type' function; you'll find that tables are used more in LoTRO, which don't allow for very detailed OOP systems.
Here's more on the subject; http://lua-users.org/wiki/HiddenFeatures