A common use for the Init function is to set default values, when the module is invoked. Imagine you have an entry, which is for a user name. This entry should be initialized with the current users name. An approch for this could be:
... set user [exec whoami] Entry username -default user
This does however not work in two situations:
In both cases. you should use the Init function:
... Entry user ... Init { set user [exec whoami] }
When the init function is called, while importing an export file, the variable loadingExports is set to 1.