Example scenario explained; 'If we were to enable ‘Requires Budget Approval' for some departments but not for others, we could in theory have two 'organisation' points, correct? One with the Approval setting turned on, and the other with it turned off, but each then applying the setting to all departments branching out from it?’

Unfortunately, Purchase Plus doesn't function in that manner. Ticking the section at the Department level won’t change or activate any setting changes.

The setting is either on or off for the whole Organisation.

Please check out this article for more information, Budget Module Overview.