I agree with diesel85's comments. I never disagree with Dave7040 who does the best research around and is way senior to me. I will nitpick Dave just a tiny bit. The Draft control sensing is on lift, not pulling force. Some newer tractors do Draft sensing on the lower arms rather than the top link attach point (which means only up/down, not pulling force.) Draft control only lets up and reduces lift at the right sensed times in order to gain a more constant depth for plow work. I had not heard that the 3 holes relate to fine tuning of Draft control but could be, I'll take Dave's word for it. To me the 3 holes relate more to the arc of implement movement when raising it and thus indirectly to the amount of lift force required of the two lift arms. For my work (and I think the majority of users) DRAFT control is never used or needed.
Anytime box scrapers come up as a topic I always inject that an hydraulic top link is so very very handy with a box scraper, allowing you to adjust cutting depth/angle without leaving the seat. At my "age and level of feeble" I essentially can't/won't use a box scraper without an hyd top link because of the excessive number of climbs up and down from the tractor without it.