If you play your video from the timeline with all the transitions, filters, and other changes present, the video out the ANALOG connections is 4:2:2, not 4:1:1. It is not clear whether the entire timeline is output at 4:2:2 or just the modified bits. But even outputting the modified bits at 4:2:2 does make a small bit of difference.

If you save the file to a DV-encoded AVI, then it is converted to 4:1:1 and you lose the extra bits of color information. Even if you then play that back on the timeline.

That might be the case, but this will only benefit you if you've
done something to the original DV file that came from your
camera since that is still 4:1:1 (for NTSC only!). So unless you've
added CGI or done heave post production this might yield some
benefit.

But ofcourse only if you are working with analog copies.