Let's imagine Group A is playing the 12th, and in the proper position as defined by the pace of play policy. One of their players hits a tee shot in the rough, and it takes three minutes to find it. He pitches out and scrambles to make bogey.
During the delay, Group B is in front. They play the short 13th quickly. Group A reaches the tee right as Group B walks off the 14th tee.
Do you really think Group A deserves a penalty? The pace of play policy says they don't. They should maybe receive a warning and be notified that they are being timed. They also, in all likelihood, will play the 13th fairly quickly and get back on schedule. However, their holdup on the 12th affected the group behind them, who had to wait a few minutes, which caused the next group to wait a bit, and the next, and the next.
It's like when a car in front of you on the highway at rush hour slows down, so you tap your brakes. The guy behind you taps his a bit harder, and the next guy a bit harder, and the next. The car in front of you doesn't slow down enough to get noticeably "out of position," and you all pretty quickly get back to being bumper-to-bumper with each other. But as the result of a chain reaction, the last guy in the line a few miles behind you ends up with a really long trip. It's how those batches of slow traffic with no triggering accident at the front of them get started.
Can anyone actually point out a group or player today who is breaking the USGA pace of play policy after being monitored and timed and deserves to be penalized? If not, does the policy need to be rewritten? And how would you write it to make it more effective at addressing slow play without wrecking the integrity of the competition?