Whilst attempting to make use of the Managed Metadata service application in SharePoint 2013 to make use of the new Managed Navigation features, I ran into an annoying problem where any time that I attempted to make a new group via the browser using the Site Settings Term store management I would get the following error:
The current user has insufficient permissions to perform this operation
I ensured that my user account, the SharePoint Timer service account were all added to the Term Store administrators.
It turns out that the Web Application Pool Service account (in my case sp_site_ap) needs write access to the Term store via the Service Application Permissions:
Once I had given at least Read and Restricted Write access I was then able to update the term store freely.