Rich, thanks for an answer with added depth.  I tried an image to compare file sizes and this is what I got:

Least Compression                                  Compression at "5"
Baseline "standard"     4174kb                           207kb
Optomized                  3778kb                           162kb
Progressive(3scan)       3671kb                           166kb   

There is some savings on file size.

Interesting.          Tom.