Because sometimes you choose the wrong output and end up with an empty file. Secondly, it is a good visual check to see the final waveform, if it’s somehow too low, or vice versa…
No brainer.
That’s not a bad idea.
Also, I think another common problem is to forget to set the locators properly. It would be nice to show a progress meter that shows the begin/end time points in the project of the region that is being rendered.