When I was a kid, the courses I played had little bushes on either side of the fairway at 150 yards from the green, give or take. There was an occasional sprinkler head marking, as well, but on some of the munis they were absent.
We used to just glance over at the bush and then pull a club. If we were close to the bush we sometimes paced it off.
Over time we got pretty good at estimating yardage. You could've just dropped me onto any golf course anywhere in the world in the middle of a fairway and I could've told you the approximate distance just by looking.
HOWEVER, now that I had a Golf Buddy range finder and have had one for several years, I find that my ability to judge distances by eye is not as good as it once was. So now I sort of DO need a range finder. I've become dependent on it. I forgot it one day and I felt a bit lost out there.
But it's a skill I once had, and could probably get back again if I stopped using the range finder. I could probably also remember a lot of phone numbers in my head if I stopped using a cellphone, but neither of those things is going to happen.