sep driver permissions

I have a customer who set up permissions on the driver 600.  Obviously this is wrong since a non-root user in the vtune group will not have permissions.

I advised to insmod with permission  660 to restrict use to those in the vtune group.  Fine.  Now their question is - does the group perms NEED WRITE permission?  Shouldn't the perms be 640 - in other words, why does a user need write permission?

Ron