The grooves along the rails as seen on SS Hazen and Stretch boards do have a function. They stiffen the rail line and I've heard folks say they give a place to grip.
If you look at the flimsy sheet metal on cars, most commonly found on doors, Detroit has found that the those indents give ridigity to an otherwise flat surface.
When place along a rail line, especially if the blank has a center stringer, it imparts stiffness towards the rail to help reduce rail twist-off.
How much does it help? I don't know, but there was an interesting observation over at Sways on the Chapstick packaging, here