This command is mainly used to confirm what DNS records exist on a particular name server for your domain.
You could use this online tool to check.
Enter your details similar to the image below.
Note that the "Server" section in the image above refers to the name server you are searching your domain on.
You should be presented with similar details below:
This tool is especially helpful when it comes to issues updating name servers. Should you try to update name servers but it fails then do a dig for your domain on the name servers you wish to update to.
If you don't see any "NS" records in the results, then the host you wish to point your domain to needs to resolve it before the update can complete.