For me sandpaper lapping was just too much trouble. I just didn't fit with the rest of my sharpening. It was too much a separate operation. A diamond plate has no set up or different requirements from my simple sharpening station.
Previously I would put off lapping for too long; leaving a lot of material to be removed. I found this to be no good for sandpaper, and sandpaper no good for this.
With a plate waiting right beside you it is no bother to give the stone a few light strokes. There is no set-up. nothing to change, no need to cross the room, etc. That is just my laziness, but I am sure that over the last few years I have saved the cost of several books of sandpaper, and it is still cutting. More frequent lapping, i believe, causes less surface wear than restoration type work required when things are obviously out of true