The less you mess with it the less chance you have of nicking the power fibers.
This is correct. I don't like the way that thin outer rind looks, and it serves no function by itself. It's just a waxy cuticle, almost like a coating, and has no strength of itself. I remove it because it is harder to stain and taking it off lets me see the bamboo better. (Bamboo does have "grain", and some of the backings I have bought had zig-zags one way and then the other between nodes. That's good to know before you start using a block plane on the sides).
However! Most of the bamboo backing failures I have seen or heard of were from someone flattening the nodes, gouging a corner of a node off to one side, picking up a snag at a node, or similar. If you sand it off, start with, like, really sharp, new 150 grit paper, not 60 or 80 grit. Or, use a sharp scraper and very light pressure. I barely smooth the nodes. Don't take them down at all.
