It means it will return None. You could remove the return and it would still return None because all functions that don’t specify a return value in python will by default return None.
In this particular case it means the code will go no further if the object has the attribute 'moved_away', without the return any code below would be evaluated even if the if statement evaluated to True.
So you can think of it as being similar to a break statement in a loop when you have a condition you want to exit the loop on, without the break the code would continue to be evaluated.
if hasattr(self, 'moved_away'): # if this is True we return/end the function
return
# if previous statement was False we start executing code from here
