Corner cutting is quite an enhancement to speed up algorithms. The way I measure my amount is by looking at the corner and compare it to the two lines that divide the face into 3 columns. If I do a U 30deg, it the corner will be exactly lined up with the line to the farthest right, 45deg would be in the middle of the middle row, and 60deg will be on the line at the left. I don't go much more than "between 30-45deg." But I do know with some force and back R R' moves I can do 60 degrees. That's a little absurd, but my 30deg is completely effortless and I know for a fact it has helped me when I get sloppy.
Yes, accurate turning will beat that, but accurate turning to a specific degree of corner cutting that is still effortless will shave fractions of a second at a time, which when you get down to the top 100 people, especially top 10, that obviously makes a difference. Look at the top 100, the list goes up by 0.01 at a time and people get matches of the same time 5 people in a row sometime. Now we're talking about corner cutting making a difference. People like me who average low 20's don't have much of an argument except the fact it can help us a little bit. People like Feliks have a huge argument.