I can be a smart a$$ and tell you to "google it", but I don't like that attitude
I came across f2fs when using devil kernel, and from readings, it seems f2fs is a new file system created by samsung to replace ext4 for mobile devices, as it is supposed to be faster, and a couple of articles claimed that it was when used on the motorola X (I think...) than standard ext4.
Basically it was a tradeoff between faster boot times (ext4) and a faster overall system (f2fs), and when I tested it on 4.3 stock roms with devil kernel, I can honestly say I saw improvement, but the whole process (special recovery, special kernel, modifying update scripts for roms not to format back to ext4 before flashing, or going through the whole ext4-2-f2fs cycle after every update) was hell, and I consider myself an above-average user.
So until it is made a bit easier or more user friendly, I'd stay away, as the performance boost is not worth the hassle for the normal-user.
just my 2cents