[SDPhantom]

This isn't restricted to just WoW. The entire file, known as the main chunk, is seen by Lua as a function. After compiling into its own binary format, Lua immediately runs the function generated. This is for each addon file, so if you need to stop your addon from loading, you need to put checks like this in all of the .lua files.

There are some restrictions to using return that follow the same rules as if they were in a function. They are required to be at the end of a scope. Note chunks are blocks of code in which locals defined within are isolated. This includes function definitions, conditional blocks, and loops. You may also force a chunk to be defined by using the do ... end block.