Unless it’s a blind curve then it takes no time to adjust to the conditions on your own And it comes naturally. I say this as someone that just drives as fast as I want and don’t usually attempt to adhere to any posted sign. In cases there is a sharp/blind curve that’s when I see they usually just use the curve arrow sign to warn me and so I know to pay a bit more attention and make sure I am ready and able to adjust my speed if actually needed. I almost never adjust just because I see a sign.

It tends to be more economical to adjust in advance so that you don't have to use non-regen brakes. (Or any brakes, in a pure ICE.)

It’s not always required. I rarely brake at all on an open road, except for stops and if something else is physically in my way.

If if the conditions actually require it, that’s when I brake. Not because a sign told me too when I may not actually need to. I feel that’s probably the most economical option.