I had the idea that maybe when you mine and 'shift' you'd be mining that brick faster because you are focusing only on one block?
I was about to post the same idea after carving out a staircase with the pickaxe. I think it would cut down on some of the "mining is slow" complaints.
I havent found that changing to mining a single block is faster than mining the 4, or 9 blocks, and with even a copper pickaxe which is very easy to get hold of, mining is fast enough.