If you are not using comms to speak with other players, then you can just buy a good 5.1 or 7.1 headphones. You won't require a headset if you aren't using a mic.
If you play competitive shooters, then in some games that use good surround sound, you can pinpoint where your enemy is. That's the difference.
It's just more immersive with a 5.1 or 7.1 headset/headphones.
A lot of "gaming headsets" come with a removable mic.