It is not about efficiency or trying not to be slow. I am not bothered how many people cut in line or "cheat".[1]
Someone will always keep cutting into the space. It is impossible to maintain 3 second to the car ahead. First one car will cut in, you make room for them and add 3 second gap the next car will cut in. Maintaining even a 1 second gap is sometimes very hard close to exits.
[1] Personally my driving pattern changed once I switched to driving a hydrogen fuel cell Mirai, slower is better on the mileage and fuel cell owners are very range conscious.
In the Midwest here and drive the same way, from rural to busy city and back. Never had any issues at all with it minus the car or five I let in front of me. I usually keep about 5 car lengths, so a fairly reasonable gap without being annoying to drivers that happen to be behind me. Also, I have zero panic braking incidents, which seem to be a big cause of crashes and slowdowns in heavy traffic due to the slinky phenomenon that tends to happen.
Not only can I see everything beyond the car in front of me, I tend to "soak" up the braking energy when there is a panic braking incident in front of me. I have no data to back this up, but I'm almost positive I've kept traffic moving much better behind me and prevented rear ending incidents using this tactic. Also, I wouldn't downplay the amount of fuel that is being saved that comes with not having to almost stop, then start over again from the slinky effect.
Someone will always keep cutting into the space. It is impossible to maintain 3 second to the car ahead. First one car will cut in, you make room for them and add 3 second gap the next car will cut in. Maintaining even a 1 second gap is sometimes very hard close to exits.
[1] Personally my driving pattern changed once I switched to driving a hydrogen fuel cell Mirai, slower is better on the mileage and fuel cell owners are very range conscious.