I am trying to understand what the purpose of using the root access restriction option is while exporting an NFS share.
As per http://now.netapp.com/NOW/knowledge/docs/ontap/rel701r1_gf/html/ontap/filesag/2nfs3.htm If you specify a host with the root option, the root user on that host keeps the root UID (0) when accessing the resource.
Doesn't the root user have the UID 0?
Clarifies it. Is there anything else that I am missing to understand?
The root option gives the root user on an NFS client full privileges on the export. Otherwise, the root user, as you said effectively gets mapped to a UID corresponding to "nobody", a user that has no special privileges.
You may use it if you want to prevent someone who has root access on a client system from making changes on the filesystem. To be honest, it is not widely used these days.