They appear if necessary, based on your settings.
For example, if you enable AI Denoiser, a DeMain box appears to be able to check the render with or without denoiser.
If you enable Adaptive Sampling, a Noise box appears, to be able to check the green processed pixels by adaptive sampling.
If you enable a pass, in render settings/multi pass tab, a box appears foe each enables pass, like with Render Layer passes.
In 2020.2 CUDA, and future 2021 Mac it is possible to create your own output box, based on a desired layer/passes/AOVs combination, very useful with Render Layer technique, to be able to mix and compose reflections, shadows and backgroud directly in Live View:
ciao Beppe