Rope drag from top roping and how to reduce that on slab?

Is it unreasonable to climb to the anchor, clip in, and then rappel down so that the climbers weight isn't on the rope as it runs over the rock? Or if top roping a sport climb, clip in to the nearest bolt and then rap down? 

Do people cut a climb 'short' (and not climb the full height, by extending their anchor pretty far to avoid certain sections of the rock that will drag?

At the end of the day, will it depend where you climb, and drag is going to be inevitable to some degree? More here, less there?

Unless it's overhanging, your rope will run over the rock. There is a point where rope drag is a concern, but your rope doesn't need to be babied. They're supposed to wear. Unless it's extreme rope drag, being lowered is quicker and more common than rappeling from the top of a single-pitch climb.

Extending the anchor to decrease rope drag is common in cragging. Case-by-case basis.

Smooth rounded slab vs sharp edges

Case by case basis

If there are sharp edges, need to pad or extend with static anchor rope

Extend the anchor as far as is practical / desired.

3 opposite and opposed non-locking solid oval carabiners can put the rope into a position closer to parallel to the face of the rock instead of 2 offset D lockers which tend to pinch the rope more against the rock face.

... if it was an institutional setting or something you would be using more than for 1 person you could get really creative and like lay down some slippery plastic edge guards for the rope to run over. Or even prop the master point up off the surface of the rock using jackets or w/e else.

What's been said so far. Plus, contribute to ASCAA. This is what's going in for anchors at single pitch crags in many locations, as well as replacement work for the thousands of aging bolts out there. By far the easiest way to make a contribution to climbing, as even dinky little one time contributions add up, and directly benefit climbers almost immediately. You can set up recurring donations too, so you don't even have to apply thought to the process.

Best, Helen

if you climb at areas with crappy slabby topouts, particularly on abrasive rock, rapping instead of lowering can save a world of hurt on your rope and help it last a lot longer.