Saw blades rolling: rolling of saw blades enables the introduction of pressure in the back part of the blade (the front of the saw blade is the part with teeth). The pressure results in elongation of the back part and slight deflection of the saw blade.
When the saw blade is being tensioned (in the tension frame) the tension is transmitted into the front, toothed, part. The saw blade saws accurately and keeps the cutting plane.
See here for more info regarding grinding and tensioning of saw blades.