I'm willing to bet I can tap the install button for a given app faster than you can scan the equivalent QR code and hit install. The challenge is for iOS.
The workflow for scanning and actioning on a QR code is tediously slow. Unlock your phone. Page over a few times (because let's be honest, QR code scanner is not getting front-page placement on my home screen), open the app. Wait for it to initialize. Hold over QR code. Nope, closer/further. Ah there we go. Bam. Now tap on something to visit site. Wait for site to load. Oh wait, it's a redirect to the App Store. Wait for App Store to load...
A sufficiently short and easy to spell URL can be entered much, much, much faster than all of the above. If it's app-related, a sufficiently short and easy to spell app name will convert me faster than a QR code any day of the week.
Most of the time when I hear about an app, I'm at my computer. So I type in the full URL to get to that link or go to the App Store's slow search. Half the time there's several search result, and I'm fighting with iPhone's spell checker if it's a cutesy name or have to remember the company's naming scheme. (For example, I searched for "Flight Track" instead of "FlightTrack" and received tons of incorrect results.)
Another good use: connecting the physical world with digital when it's not practical to set up a short URL (think a church having a silent auction, with in-depth descriptions listed on the website)