Before you execute any of the SharePoint Cmdlet you must be sure that you have necessary permissions to execute in the farm. Also you must have access to local WSS_ADMIN_WPG group where you are executing the cmdlet. Also you must be member of the SharePoint_Shell_Access SQL role within the databases your cmdlet calls in to interact with. Some commands also require you to be a member of the local administrator and farm administrator grooups. For ex. to create a web application, you must be a local administrator and farm administrator.
In Regards to adding users to the WSS_ADMIN_WPG group and SharePoint_Shell_Access SQL role, you must not be adding users directly to these groups rather you should use Add_SpShellAdmin cmdlet. This cmdlets accepts optional database name as parameter. If you do not pass this parameter it will add the user to the SharePoint_Shell_Access SQL role in the SharePoint configuration database only.
Above third line of code, it will add Add_SPShellAdmin SQL role in all the SharePoint databases including configuration database. Also you must be farm administrator and you must have securityadmin SQL role in order to execute this cmdlet.
- Use Remove-SPShellAdmin to reveke access
When it comes to removing access you should use the above command to remove permissions, however it will not remove access to the user from WSS_ADMIN_WPG group on any server. You should remove this access manually. I recommend you should create “SharePoint Shell Access” AD group or groups if you want more fine grained control and grant these group Add-SPShellAdmin access there by avoiding the case users retaining the rights, where they shouldn’t.
When we get to the point where we need to execute scripts you may have to set execution policy to allow scripts to run. You could do this using Set-ExecutionPolicy by passing the execution policy.
- Set-ExecutionPolicy -ExecutionPolicy Unrestricted -Scope Process
While setting policy for production farms I recommend using policy scope to Process so it does not persist other PowerShell instances.