It identifies you to other players in multiple games, including Minecraft. There are ways to change your Minecraft name on each platform and also on the Java and Bedrock editions.

Depending on the version being played, fans of the game are just a few short clicks from a fresh handle and new possibilities. How To Change Your Username in Minecraft Using Microsoft ...

"Minecraft" offers cross-platform play for both versions of the game — Bedrock and Java — but you can only play with users who own the same version.

Minecraft Java edition beta version There's a little bit more that's in the current Java snapshot version, as it's the only version at the moment with all the new mountain biomes.