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.