I have tried that, taking a break after the front 9 but for me it always seems like I completely lose it on the back nine if I do that. Only once did my back 9 even come close the being as good as my front nine after the break. For example i was -2 after the front 9 at St. Andrews in one of my first qualifying attempts. I took about an hour break. The back 9 was a disaster from # 10 which was a triple bogie until # 18. I think I shot something like a 48 on the back. Not even breaking 80 for the round. A later qualifying attempt I was - 6 with 4 holes to go and stopped for 15 minutes. Big mistake. As well as I had played the first 14 holes 3 birdies on the last 4 holes was not out of the question and i could have had a chance to qualify. When I came back I went bogie double bogie double bogie and bogie to end up even par.
But also about playing too many easy 9 hole rounds. Like the front 9 @ St. Andrews. After 6 months or so on here most of it as a pro I decided it was time to make master and one Sunday after noon I played 4 or 5 ranked rounds on the front side of St. Andrews and made master but as you can see by my average now it may have been a mistake but I think I am improving once again. It just seems that I lose concentration on one or 2 holes per side and what was a great round turns into a so-so round if not a completely awful round. But one thing that is really improving for me is the speed control on the very fast greens. My putts almost always go very close to the correct distance. I just can't seem to read the greens right. That part does get frustrating. To have a 30 foot putt hit it 30 feet and be something 5 or 6 feet from the hole because you read the green so poorly. Frustrating because I know it is me who is to blame.