[NumberWangMan]

I believe that if you're doing some heavy chopping, that orientation keeps the cutting board in good condition for the longest time, as you're not cutting through the wood grain and taking chunks out of the board.

Separately I've heard that while bacteria can live in wood cutting boards, they tend to stay where they are rather than migrate out of the board and into the food -- but I can't back that up with any actual references.

[datavirtue]

Bacteria needs moisture. It ain't clean until it's dry.