Why the rook only matters always.
This piece which sits at a1 or h8 can only means trouble for those who are not acquainted with it. One's acuity with it will prove their mettle. To begin to use this piece may seem nascent when one starts leading with it. Some can recidivate into the standard barnes or queens gambits when they find it's usage difficult to master. Only after churlish play one can find real congruency in their use when pairing with pawns and at some junctures even knights in opening.
In short it is the gas.