They're adding the ability (which Xbox One has had for a while) to play games off of a connected USB hard drive, as well as Boost Mode for older PS4 games on the PS4 Pro (which I don't have).

I like it because I've been a member of PS Plus for long before I actually owned a PS4, and thus I have download rights to 100+ PS4 games. The built in 500GB drive just wasn't getting it done for that, so I bought a 2TB drive which I formatted to exFAT (like the PS3, PS4 doesn't get along with NTFS format) and have all hooked up and ready to go.

Neither feature is especially helpful for me (og ps4, no spare external hdds) but those are both excellent additions for the people who will make use of them.

The low hdd space has taught me to plan in advance for what I want to play, so I'll start downloading large digital titles the day before I actually plan to play them, lol