TeeTime wrote on 8/11/2012, 5:49 AM
Well, according to the handy help feature in Vegas:

Real-time render is a playback mode that renders your project to .wav format. Real-time rendering allows you to include the output from an external input source such as an effects processor with your project.

Chienworks wrote on 8/11/2012, 12:34 PM
To emphasize, it's useful for audio. It won't have any use for video. Well, at least not until PCs get to be about 20 times more powerful than they are now.
Marco. wrote on 8/11/2012, 1:19 PM
I always found and find this naming very confusing as it pretends to be a certain kind of the regular render function just happening in real time.