This is s nice new feature I just discovered. Actually the soon I downloaded a new app on my PC I got a message on my iPhone saying I can enable automatic downloads for new purchases on other devices. What it means is that when I purchase an app from iTunes on any of my devices for example PC, it will automatically get downloaded to my other devices such as iPhone or iPad. I think this is a useful feature because I then don’t need to connect my iPhone to PC and Sync every time I want to synchronise my newly purchased apps.
You need to enable this feature by going to
Settings> Store > Automatic Downloads
And set the Apps or Books to ON.