This subject ties in nicely with the use of range finders and yardage markers to determine distances. I think it's both fun and valuable to play without yardage information from time to time. You've still got three ways to estimate yardage:
1. Knowing the length of the hole, you can estimate how far your first (and second) shot went, and subtract accordingly, based on previous experience.
2. Using your eyesight, as discussed here, you try to determine the pin's location. I believe a very keen observer would begin to discern subtle differences in distance, if distance information was not readily available. As we've discussed before, a flag 100 yards away looks twice as tall as a 200 yard flag. The golfer's eyesight would then become much more important, and nearsighted players would be at a huge disadvantage.
Mark, please don't have different size flagsticks. That just kills me, even when I know how far it is.
3. If it's your home course, you begin to recognize how far you are from previous shots played from the same location. The home course advantage would be greater.
Back to the topic. The 13th hole at Ballyneal has a large bunker in the right center of the fairway that looks like I should worry about it, but it's out of range for me, about 300 yards from the men's regular tee. It's very large, so it looks closer than it is. Also, bunkers are usually positioned to be in play for a solid drive, especially from a second tee which is 80 yards closer than the 510 yard back tee. Expectations play a role when visually analyzing the shot.