Someone wants to do something to database or it's server and they always ask for "Admin" privileges. Often on questioning it turns out they need to add a column to a table, so you grant db_owner on the database.
But sometimes they really do need elevated privileges on the server. You could grant them 'Local Admin'; Computer Management > Local Users and Groups > Groups > Administrators. But this give god like access, and if it is a shared server, can lead to major issues.
Using a "Windows Server 2012 R2 Standard" OS as the example. There are about 25 options. The descriptions are less then helpful.
Power Users are included for backwards compatibility and possess limited administrative powers.
So what can they do? No idea...
I Googled around looking for a list of actual powers granted for all of the options and have not found anything. There is a good list for SQL Server-Level Roles, but I am not finding anything like it for the Windows Server OS.
Clarify The description for "Power Users" is included as an example. I am not looking for it's privileges in particular. I want a list I can look at and compare to what the client needs to do, so I can grant the least privileges required