I used to use dubbin on the soles of my shoes, which helped keep the leather soft and gave a bit of waterproofing. Note that dubbin, or any grease, used on the soles of shoes will leave big black marks on carpets (but not on office carpets!). These days I usually get 'topy' or rubber layers on the leather soles, so the dubbin is redundant.
I would never, ever use it on the uppers. In WW2, British soldiers were told to use dubbin on their field boots, but normal polish on parade boots. The two substances don't mix and compromise each other's strengths.
DD