shaving a tire is for racing. it's to get more of the rubber to contact the ground with an agressive camber setup.

not shaving your tires, they will eventually wear to an even footprint on the ground, which typically means more inner tire wear.

the tire footprint (area of contact on the ground) is effected by the inflation, alignment settings, contour/construction/tread pattern of the tire.

to summarize.

if you need the highest levels of grip right now, shave your tires. If you can wait and want more miles out of your tires, dont.