Question Best usage for [realtime] Reflection Planes

The reflection planes are clearly very useful for mirrors etc. but no help is given to optimize them.
For instance they update every frame by default, even if frustum culled or facing away from camera (or scene is static).
-So you need to update them on demand and check visibility manually it seems (have added to good effect)
-They have a fixed resolution, but you could perhaps have a dynamic resolution based on size on screen?
-No visible render options to reduce render cost on reflections compared to main view?
-Also updating multiple planes every frame is obviously very costly but there is no work around as any dropped reflection frame leads to terrible update lag onscreen, there may be methods to handle every-other/staggered frame updates smoothly...

- Edit: Also Sphere reflection probes are VERY slow - updating one every frame will halve my frame rate in the editor! I thought there used to be a staggered 1-side per frame update mode which would be useful if still 6 sides

 

From my experience with HDRP: You cannot really have more than one real time reflection probe in your game. Each probe will cut the fps into half. So if you already hit 60 fps without any realtime reflection ...

 

Side tangent:

HDRP should really invest in a state of the art SSR. Last time I tried HDRP's SSR the results were so artifact ridden, I thought my GPU was dying.

Even on static scenes, you really need something to ground the reflections a bit. If Unity's SSR wasn't so horrible (as all implementations have been so far), people wouldn't be reaching for the planar reflections so often, which should be used with great care.

 

Yes indeed which is a bit crazy - maybe simpler shaders should be used in reflections & multi-frame update, I do not see any control except size. If you have mirrors/planes you can update a few of them for price of one sphere probe (which can be rendered once only for simpler static reflection)
I think SSR is too limited, ray traced is coming...