Trail braking is method of exploiting the traction available at the tires in the most efficient way possible. A useful concept from car racing is the "friction circle" or "traction circle". It doesn't carry over completely to bikes, but it's good to understand the concept.
https://virtualracingschool.com/academy/iracing-career-guide/second-season/the-traction-circle/
So, what we're trying to accomplish in trail braking is travelling around the friction circle, as close to the perimeter as we can get. When you first hit the brakes for a corner, it's not too hard to get the tire right on the edge of lockup. At that point you can't turn the bike at all, because you're using all the available traction and if you introduce a side load you exceed the tire's capability. You could let off the brake completely and then snap the bike over to max lean. Two problems with that. First, there's that transition time where you're not utilizing most of the available traction. Second, you're porpoising the bike on the suspension, the front end rising as you let off the brake and then compressing as the lean angle increases. That varies the load on the tire, and with that the traction.
What you want to do instead is let off the brake at about the same rate that you're increasing the lean angle. That way you're travelling around the perimeter of the circle, not wasting traction that's usable and keeping the front suspension compressed roughly the same amount.
On the track, the practical consequence is that you can brake much deeper into corners since you don't have to have all the speed scrubbed off at the turn-in point. Also run a bit more lean angle since you've been smooth on entry and the chassis and suspension aren't upset.
Important to realize that if done correctly, you are always releasing pressure on the brake lever throughout this process, never increasing it. If you do have to increase braking, perhaps you get cut off or someone crashes in front of you, then you also have to stand the bike up a bit to keep the sum of the forces below the traction limit.
That's all well and good on the track, but what about the street? There, IMO, the technique is a lot less useful. There's a lot of risk in feeling your way to the outer parts of the forward quadrant, if you go over the line the front folds and you crash with little to no warning. (unless you're Marc Marquez
) If I'm riding at a brisk pace I do it a little, mostly to keep the suspension settled. I don't have much interest in exploring that part of the traction envelope on the street. I do maintain just a bare amount of pressure on lever all the way to the apex. That makes it easier to be very smooth in increasing braking mid-corner if there's a need to.
I never, never use the rear brake when riding fast. Much too difficult (for me at least) to modulate it effectively.
As for "entering too hot", most street riders end up in that predicament because they're on the wrong line, usually a too-early turn-in point, especially on left handers. If that's happening to you more than extremely rarely you need to figure out why.
