Somehow it’s popular in the US, but not in Italy, Germany, Netherlands and Switzerland (it’s where I went racing and had instructions).
I only feather it in tight slow maneuvers. At speed, proper distance from other vehicles is the best defense.
I would add, dont be a speed demon, BUT, its also best to be the fastest overall in the road. Its safer to be constantly slowly passing vehicles than being overtaken from the rear and getting pinched between two cars. Ride past congestion snd find open pockets of road. Never wait between two cars in a red light, split up to the front regardless of law, its safest.
Most deaths happen when a car left turns infront of you at an intersection and tbones you. Slow down at all intersections and try to use other cars as screen cover for your bike. They DONT see you. Ride like you are invisible.
If the brake lever can reach the throttle grip, that's generally a roadworthiness failure - old brake fluid or other wear and tear in the hydraulics. Fingers getting in the way isn't short of it. I prefer a fairly sharp bite point some way out from the throttle grip and adjust the lever accordingly.
If you are planning to brake, and you should be in a racing scenario, then four fingers gives you more control. But if I'm filtering through traffic in London, I've got two fingers on the brake and two fingers and a thumb on the throttle. I also have fingers on the clutch lever. An added bonus of keeping a couple of fingers on the brake is to help maintain throttle position to stay within the speed limit over potholes and speed bumps.