This macro calls the function modu_UnloadAllModules. This will unload all modules that are not active. Because this macro is called by an extension that is a module itself the calling module will not be unloaded.
A module is active if there is a function called in the module and the module did not return from the function call yet. Typically there can be only one active module at a time unless some modules call each other in tricky ways through the ScriptBasic module calling functions. Therefore calling this macro practically unloads all modules but the very one using this macro.
See also besUNLOADMODULE.