Resin Pads.  Are used after the surface has been totally cleaned and smooth.  Depending on the initial condition of the floor, the Metal or Semi-Metal Pads may first have to be used.  Resin pads are designed to abrade the scratches left from Semi-Metal Pads.  With the diamonds exposed on the surface of a resin pad, deep scratches are quickly sanded away by the diamonds that are suspended in the plastic matrix.  The plastic matrix is what gives the resin pads their less aggressive nature or polishing capability.

While it is true you can hone with a coarse resin pad, they are not really designed for this task (or step) as they will quickly wear under this circumstance.  As you progress through the series of Resin pads - increasing to the finer grits - the pores of the concrete are progressively closed to ultimately result in a mirror-like finish.  The multi-step process provides you with the flexibility to choose how many steps you want to achieve the desired finish.