Yes. There is a reason.
The material that started out as DV AVI will not be any different, but there are materials, like photographs, that will not look as good if you encode to DV AVI before transcoding to MPEG2.
Is it important? Not usually. Not for most people. But if you want to avoid that one generation of loss, then encode directly from the timeline using the original material, and not the DV AVI it was encoded to for preview purposes.
Many people prefer to export a DV AVI and then let Adobe Encore do the transcoding.
Steven
Adobe Premiere Pro 1.5 / After Effects 6.5 Pro https://www.stevengotz.com
Learning Adobe Premiere Pro 1.5 https://www.lynda.com
Contributing Writer, PeachPit Press, Visual QuickPro Guide, Premiere Pro 1.5