This is currently hidden in the Timeline panel > Effects. Adding it to the Effect Controls panel will make it more obvious to users. Most people do most of their effects fiddling within the Effect Controls panel than in the timeline. (Probably?)
This should be added at the bottom of every effect (like the current placement in the Timeline panel.), and default to closed to save vertical space. (See attached mockup) Putting it at the top might make someone think these render/calculate before the effect.
Setting Compositing Options’ Effect Opacity to 0% renders/calculates faster (as in, always 0ms) than similar parameters within effects that control their own opacity, like “Blend With Original”. (In my limited testing 😅 )