Over at Dynamics Corporate Performance Management Char Gust asks Why would I use Main Account in a Reporting Tree?
Why would I use Main Account in a Reporting Tree? – Dynamics Corporate Performance Management – Site Home – MSDN Blogs
Install, Upgrade & AdminMicrosoft & the GP Ecosystem
Archived post from 2012. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.