This is a super important detail that is often done wrong.
2009 International Residential Code:
Sidewall step flashing min 4 in. high & 4 in. wide, length
Sidewall flashings must terminate in kickout flashing F56 [905.2.8.3]72
A lot of water gets directed down where the sidewall and roof-line meet. When this is skipped water can run behind the gutter often causing significant damage.
Here is a short video demo of why it is important