There are a few reasons:
1. Root user is the highest permission user as an administration. With root access you can basically perform changes to your Linux server system configurations/files that can:
a. Delete all the system files
b. Stop services that could render your server to go down and not able serve service to clients.
c. Running installations of malicious codes that can introduce exploits/attacks.
d. Delete or reconfigure partitions accidentally....
and many more....
So, good to know and be familiar with Linux in order to administer a production Linux server with root access. If your a home user and are setting up a test environment. Feel free to do whatever you like. Nobody is going to stop you
So basically, depending on which situation you have root access to your Linux servers.