Differences between "Save game" and "Game Instance"?

Hi, I’m pretty new to UE4, and I’ve been working on a multiplayer game where I have the starting menu and subsequent menus set to save and load data chosen by the player to a “Save Game” object as per this for example which will then affect the player’s character once they spawn. However, I’ve noticed recently the “Game Instance” class does much the same thing (eg. here).

So my question is- how are they different? I know “Save game” saves directly to file, so I would imagine Game Instance would be faster, but other than that, does one behave particularly differently than the other? Since my game is multiplayer should I prefer one or the other due to replication concerns or something of that sort?