Imagine, you are assigned a task to apply a Service Pack to an existing SharePoint farm, and as you know to apply the Service pack and run the SharePoint Products and Technologies Configuration Wizard properly you need to install it using the Setup User Administrator (Basically the user account which was used to install SharePoint). But there is no documentation and no one remembers which account was used to for the installation. So the quickest option way to find out would be go in Central Administration site
check the users in Farms Administrators group. But to your surprise there is a list of users out there and you really cannot figure it out which one is the setup user. There was a user who was stuck in similar situation on one of the forums out there.
To find the Setup User Administrator account is to check the Account under which the Central Admin Application pool is
running in IIS and also the Windows SharePoint Services Timer is running.
1. Central Admin Application pool Properties
2. Windows SharePoint Services Timer Service Properties