I've been going through the MS Cert 70-667 training kit and one of the exercises was to run:
Get-SPWebApplication -IncludeCentralAdministration | Get-SPSite -Limit ALL | Get-SPWeb -Limit ALL
This gave me access denied errors
I made sure to give the SP_Admin account powershellAccess to all content databases in SP but that didn't work.
The only thing that did work was when I followed these steps Which was basically to create a new managed account with SP_Admin and change the Service Account Farm Admin from SP_Farm to SP_Admin.
I'm concerned about least privileges permissions now and I'm not really sure what the impact of this change is.