Its got nothing to do with engine RPM or power control. It is normally wide open (I know the part diagram is just that, but if you look the plate is vertical, fully open at rest, that’s how they are.) During EGR operation and regens is when it’s used to create a pressure drop in intake so it can pull exhaust gas through egr cooler/valve.
Intake heaters can be used in place of glow plugs (think Cummins did/does use them?)
Daferris, 6.4s and 6.7s have them as well.
Hope this helps, not trying to be smart a$$
(can search for diesel egr and dpf operation for more info)