Are you saying that using current safety procedures the rotating bezel has no use? The only thing I can see that it is good for is keeping track of elapsed time, in which case it is the first 15 minutes that are graduated, which doesn't seem helpful at all. I can see a use for elapsed time, but having the first 15 minutes be graduated seems silly, unless I really am just not getting this.
today, most divers don't even wear a watch as a timing device any longer... they use a computer that times the dive and computes the bottom time available based on a multi level dive profile. but that wasn't your original question, the red zone or the first 15-20 minutes usually marked in minutes or red is useless and is basically just a nod to the past (Navy method countdown ascent timer) and holds no significance at all.
particularly with recreational divers.
the counterclockwise rotating timing bezel
however is still a fine backup timing device to a computer in general.
lets say using the dive tables you've calculated your profile and you are able to dive to a specific depth for 35 minutes. before starting your dive you simply rotate the bezel where the marker ^ points to the current position of the minute hand.
you know the amount of bottom time the tables said you had at the planned depth, you dive your dive periodically checking the elapsed time by counting the minutes indicated by the marks/numbers on the bezel and with all factors considered you make sure with the proper ascent time and rules for safety stops that you return to the surface in the original calculated allotted time.
now we have computers that calculate all of that without having to really refer to dive tables because all of that is figured in the computer along with actually knowing how deep you are, when your dive started and how long you've been down, even figuring multi level diving profiles for more accurate calculations. some computers are air integrated and figures everything down to how much nitrogen you should have accumulated in your blood.. that's the main purpose of all of this timing is keeping track of how much excess nitrogen or oxygen you have accumulated and allow for off gassing before reaching the surface again.
note: the timing bezel just keeps up with the amount of bottom time you have calculated with the dive planner (tables) at the depth you planned to dive, it does not keep up with how much air you breathe from the tank, for that you have to monitor your tank pressure gauge.. so there's many reasons why just anyone can't walk up and rent a tank and jump in the water, a proper underwater scuba training course is needed to understand fully the inherent dangers of scuba diving.