If you read the keyboard page then you’ll know that I mentioned that I play Osu but never really explained what it is.
Osu is basically a rhythm game in which you have to click circles at the specific beat of a song (I bet you can see where I’m going with this in a gaming headsets page) and just imagine how atrocious this would be without proper high definition audio blasting straight into my ear! Impossible!
And while this is not the case for most games, you have to understand that sound is just as important as visual cues within any game (at least a game that’s worth something and decent). Taking League of Legends as an example, many of the indicators that you see about things happening are a combination of visual animations but also sounds, all sorts of sounds and communication goes on while you play that you must pay absolute attention in order to make sure you perform the best.
Last but not least there’s something that you will see as the most important thing ever, which is communication, team communication using proper high quality gaming headsets will ensure that no message is lost, maybe normal headphones won’t make you misshear messages but remember that while you play with someone you have to listen to them while still listen to the game audio cues that tell you the situation of each game, using CS:GO as an example you can rapidly tell the importance of both the in-game narrative, effect sounds as well as your team-mates during all times, this is why high definition audio at all times is a MUST if you want to be decent at any game.
Using an external microphone instead of a full headset is up to you however there’s no way of comparing the convenience of a microphone right next to your face compared to something you install on the desk.