If onUpdate() calls would allow differentiating between updates that are required and that are optional, it would allow avoiding unnecessary repainting.
For example, if a watch face does not require updating every second (by showing just HH:MM), then 59 repaints every minute in high-power mode go to waste.
On the other hand, if the OS wipes the screen clean for some reason, then onUpdate() obviously must execute.
The request is to change onUpdate to include an extra parameter to specify if the update is optional or not:
onUpdate(dc as Graphics.Dc, required as Boolean) as Void
This would help writing more power-efficient code.