Does the prerendering useful when rendering final video output even if it is just uses a few frames? Does Vegas use it when rendering previews? Maybe like Premiere does? Thanks. Correct me if I'm wrong.
As far as I am aware, making a Selective Prerender has no effect on the final render. It is used during preview to be able to preview at a high quality at normal project speed. Note there is no audio included in the Selective Preview, when previewing the Selective Prerender Vegas pulls the audio from the timeline audio track.