A few questions on Game Centre...

1)  Is there a reason I would report an achievement as less than 100%?
2) In the 'Report Achievement___' do I put the Achievement ID as set up on iTunes Connect?
3) What is the proper usage for the 'Show Banner with Title ___ and Message ___' block?
4) Is typically best to just use the 'show achievements' block upon completion of the game or end of significant go?

Thanks