If you are a restoration purist, then stop reading now. I added a vinyl sweep to the bottom of the south side door. Originally the wooden door simply met the wooden threshhold. But the sun, rain and snow caused the door to expand and contract to where there was a gap between the door and the rotting threshhold. So after having replaced the threshhold with a nearly identical one, the gap was improved but still subject to fluctuations in humidity.
The most nerve racking part was making the cut. There's little to do if a 100 year old door is suddenly cut too short. I measured about twenty times and used a piece of plywood as a straight edge cutting guide. But all turned out well, and now the door doesn't stick or scrape. I also put the second coat of paint on, so here's a picture of the final product. Only thing left is to make the 1" square trim pieces to cover up the caulking around the frame. They aren't an original feature but they make perfect sense and help give the door and windows a "finished" look.