The watching the grain thing is something I learned from a friend, Margaret Doucherty (little brown bird)
I asked her why the book instructions had us cutting the background block with bias edges (picture cutting all those 'on point' from the fabric).
She said consistent grain line throughout the whole quilt is one of the things the big show judges look at after they get entries narrowed down to just a few. And her border was on grain so the applique blocks needed to be also.
Just something to think about if you do head in the direction of big competitions.
Tessagin, the chalk line across the fabric is brilliant for both grain and side issues.