Update #2: Naughty Dog Community Strategist Arne Meyer posted the following on NeoGAF:
Alright all... rewind a little. (also why does this always happen when I'm not on a PC but on my phone?)
Improved shadows in 30 are added as part of the patch. As we were finishing up the day 1 patch we were looking at the game and released at 30 we had extra cycles we could do some further, unplanned, graphics enhancements - and that turned out to me shadows. Naughty Dog being Naughty Dog - we couldn't let idle rendering cycles stay that way! :)
Shadows at 60 are absolutely improved over the PS3 version and the game just looks and runs best at 60. The improved shadows at 30 are a nice bonus - but seriously, not reason enough to play at 30 unless you already needed or planned to lock it... well, it does help a little when you are in Photo Mode, but you can enable that at last minute.
Stick to 60 unless you have to or really do prefer 30. that's why 60 is the default!
Update #1: I've been receiving a ton of questions regarding this article, and want to address a couple of them. For one, even if you have the 30 FPS lock disabled, you are going to get a much better visual experience with The Last of Us Remastered than the PS3 version. This PS4 version has native 1080p resolution, higher resolution character models, improved shadows and lighting, improved level of detail, and longer draw distances.
For those of you worried about whether or not Naughty Dog has taken advantage of the PS4's hardware, you really need to play the game to see how much work has gone into this remaster. The truth is that no matter what the game or platform, when you change the target framerate from 60 to 30, you open up resources. Naughty Dog decided to go out of its way to take advantage of these extra resources when the option is enabled. If anything this should be applauded.
Additionally, yes, you can change this setting on the fly. This is what the option looks like under the Display settings:
Although the embargo lifts in a few days—and our review will be up at that time—, I'm going to take this opportunity to tell you that this is single-handedly the best looking console game I've ever played, with or without the 30 FPS lock enabled. You are in for a treat.
Original Story: We've just received our review copy of The Last of Us Remastered, and can confirm that there's a benefit to playing with the 30 frames per second lock enabled (accessible via the Display Options). If you enable this option, not only will the frame rate never dip below 30 throughout your experience, but "higher quality shadows in-game" will be enabled.
So, you have a big decision to make. Do you play the game at 60 FPS? Or do you play it at 30 FPS with a better visual experience? If you decide to play without the 30 FPS lock, the framerate may dip below 60 during certain sections of the game. However, based upon our experience with the title today, we can say that if you are a fan of 60 FPS, you won't be disappointed. This is a port that looks amazing and is highly optimized. I mean, this is a Naughty Dog game, after all.
Related: The Last of Us Remastered Review
No matter what you decide, the game will run at 1080p, meaning there will be a million more (twice as many) pixels on screen when compared to the 720p PS3 version of last year.
If nothing else, this option serves as a great way for you to see the difference between 30 and 60 FPS, and something for you to play around with to determine if you prefer a higher framerate or better visuals—don't underestimate how important shadows are.
This option will be added in a day one patch that also brings along with it a Photo Mode, a 'The Making of The Last of Us' documentary, bug fixes, increased install speed, and and improvement to remote play.
The Last of Us Remastered Screenshots