I wasn't super diligent in keeping analytics for my website, but each app would have maybe 1 click every 2-3 days, and the big blue button I used to have for all of my apps had about 5 per day. Overall, very little traffic from my website. It was mostly about less work for maintenance when I built new apps.

You probably already know, but for the benefit of everyone else: if you're advertising an app, when you create a new ad, make sure to select "App / digital content ad" and then "App promotion ad". It will do all of the OS targeting for you and pull in your app icon, name, and URL automatically.