Cutting diagonally is essential right now. My large cutting mat is stored upright behind my bookcase. Perfect - flat, invisible to childish eyes and easy to access. Except. Last time I put it away, it cartwheeled. It's now far out of my reach, behind the bookcase. Which is full of books. It's a big bookcase, and I have a lot of books, so each shelf has books, with another layer of books on top of those, and where the books are narrow enough, there's another row in front, and another layer on top of this row.
So I'm cutting diagonally, because my 'class' mat isn't wide enough for a fat quarter. Still, the blade is sharp, the children are at school and the sun is shining. Things could be far, far worse.