Is there technically any reason why I should use onRestoreInstanceState? Could I not do all the restoration in onCreate by checking if the savedInstanceState bundle is null? What is the primary benefit of using onRestoreInstanceState over doing everything in onCreate?
This method is called after onStart() when the activity is being re-initialized from a previously saved state, given here in savedInstanceState. Most implementations will simply use onCreate(Bundle) to restore their state, but it is sometimes convenient to do it here after all of the initialization has been done or to allow subclasses to decide whether to use your default implementation.
onRestoreInstanceState guarantees you receive a non-null Bundle object also in the lifecycle of activity it's called after onStart
But onCreate: you should always check if the Bundle object is null or not to determine the configuration change and as you know it's called before onStart
So It's all up to you and depends on your needs.