I used to vary my stem height (always same quill stem and mo more than a cm change at a time) in my racing days. I started the season with the stem up around 1 1/2 cm. It gradually came down as the season went on. For criteriums when I was in form, it got slammed. Up about a cm for 4 hour races.
Now I do not race and have several bikes. I keep the reach roughly the same on all. (Fix gears get the position rotated forward, seat forward, stem longer and lower for the same reach and back/thigh angle but a more aero position for the inevitable slogs upwind in too high a gear.)