Neil Brown, Sony's R&D senior team leader, shared in a few words a significant feature for the PlayStation 4 during the Develop conference (without needing an DRM, Microsoft):
You can visit your friends house [and] you can log into your account and play any game from your digital library, which is good. But how useful is that if it takes half a day to download the game you want to play? With Play As You Download you get much quicker access to at least the first section of the game so you can start playing quicker. So this makes a digital library a practical option in the real world.
Thus, you can access all your digital titles on a friend's PlayStation 4 and play them immediately. You don't have to waste time waiting an hour to start playing, and you don't ever have to worry about leaving your disc behind or have anyone spill Red Stripe all over it. (You know who you are, buddy!)
As such, this is an assured incentive for players to purchase digital titles and have friends that will let you try out games for free with a shared account. Now, hopefully you can establish a specific circle of friends or family that can share the titles on your account without requiring you to sign in.
The main difference between the Xbox One and PS4 here is that while you still need access online to even download the game, the PS4 version can be played offline without an internet check. Also, there's no connection between required online check-ins with the share feature.