I have seen some outrage over this whole 9+6 thing but think about it if someone comes up to you and is like "QUICK! WHATS 9+6?!" its very likely you will at that moment have to quickly count in your head "9, 10, 11, 12". But if you teach kids that 9+6 is the same thing as 10+5 it will become apparent to them that 9 + 6 isnt just that. Its 10 + 5, 8 + 7, and a massive range of other numbers it could add out to.
Its teaching kids how flexible numbers really are and that whatever numbers you are looking at that need adding are also other numbers in disguise. Its just a shortcut showing numbers have different identities that once learned is actually very useful.