[tomtang0514]

If they already have the apps installed they're "converted" customer who don't really need advertising anymore. But how to get them know the app and install it in the first place? Ads impression is a common way beside recommendation from friends.

Additionally, most advertising are about pushing people to buy product like snacks, beer or cloths. I doubt many people really install a Zara or Gap app or put the website in their bookmark.