If I am converting an avi or mpeg file to DVD Compliant mpeg2 using TmpegEnc, why would I demultiplex the file into separate audio and video streams, i.e. mp2 and mv2?

The reason I ask is that I see many posts advising this process. My final objective is to burn a DVD-R or +rw. I usually just import the compliant mpeg2 into SpruceUp for authoring which creates my VIDEO_TS and AUDIO_TS for burning in Nero. Am I missing something, is there a benefit to doing this?