From an architectural perspective, no one has mentioned the impact on design.
I usually ascertain how the owner will likely mow the greens. If it is triplex, I make sure the bunkers are at least six, and preferably eight feet off the putting surface. Actually, I draw them about five feet, because is seems that dozer guys build both the green and bunkers from the inside of the stakes, and try to leave the stakes standing, meaning that the bunker usually unintentionally "creeps" about 2 feet away from the green during construction.
From a good player's perspective, bunkers 8 or more feet off the putting surface really don't impact play very much, but do tend to trap the higher handicappers. For a real test, it's best to have the bunkers as close as possible, which may be what TEPaul was driving at originally.
However, even if the owner insists that the green will always be hand mown, I am sometimes reluctant to put the bunkers within a few feet of the green. I always wonder if the decision is being made with a time perspective - that is, in the next recession, will we be forced to go with the economies of riding mowers, despite our best intentions? If you don't leave turning room, you are stuck with hand mowing.
Perhaps the ideal solution is for Toro and competitors to continue to develop really light weight riding mowers, so we can have the best of both worlds.
Of course, the actual turning room depends on the operator as much as the equipment. I worked golf course maintenance for a few summers in college to prep for my eventual career, and I occaisonally put a riding greens mower in a bunker adjacent to a green, even with about 12 feet of turning room, but with a tricky bank.
Worse yet, I was in charge of mowing some University of Illinois turf test plots next door with a hand mower. On my first attempt, I put the mower through a fence and almost into the Des Plaines drainage canal, despite about 20 feet of turning room!
(What were those instructions.....pick up front of mower and then release the drive cluth, or the other way around? D'OH!) If you can picture the cartoons with the siluohette of the roadrunner's nemesis, Wiley Coyote in a wall he has just gone through, you can picture my predicament that day!
Handling those mowers can be tricky, and don't think for that those guys out there working on your course are merely "grass cutters" as they are running some high tech equipment for your benefit and there truly is a science to everything.