What significance does the user/host at the end of an SSH public key file hold?

Basil A asked:

I can’t figure out why does an SSH public key file generated by ssh-keygen have a user and host at the end of it.

Example: id_rsa.pub

ssh-rsa ... rest of file ... /CA9gyE8HRhNMG6ZDwyhPBbDfX root@mydomain

Notice the root@mydomain at the end of the file.

If I can use the public key anywhere with any user to authenticate using my private key, what significance does the root@mydomain have on the authentication process?

Or is it just a place holder to figure our who was it issued by?

My answer:

This field is a comment, and can be changed or ignored at will. It is set to user@host by default by ssh-keygen.

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