Is Nier Automata on steam the online game?

I don't really know how steam works, but I'm interested in playing this game (like super interested, and I don't own a PS4). I'm not interested in playing with others (I'm more of a single player kind of person unless it's games such as smash, mario kart, etc.).

I was listening to the soundtrack on youtube (which by the way is beautiful), and I noticed this one comment saying, "Thanks to all those who gave up their save files." What's this all about? Why are people giving up their save files?