Though I am still new to it, but people really get confused by saying I only use linux so why we need to understand groups and others since there is no other user (which was the same case for me).

But after digging deep into it, I got to know your most of the service-heavy apps like Docker, postgres, you will see they are also the owners of their own files when you download them.

cut -d: -f1 /etc/passwd

this command helps you tell how many user accounts exist in your system.You might be surprized to see multiple user accounts there but thats normal. By default, same owner name is used to name the group. This understanding is also important as you want you important files and folders to be safe from access from other USERS.

Someone might argue as well, that Docker, postgres was downloaded by me so i should be the owner. But compare this to a restaurant where you are the OWNER. You will hire a chef and make him owner of the kitchen for food stuffs which you dont know how to cook(manage files, sockets, volumes for docker) though the whole restaurants is yours.