One business unit or twelve? There is no default answer and the documentation will not give you one, so this lesson gives you a way to decide.
Start with what a business unit boundary costs. Each one is a separate configuration surface: its own Payables options, its own Receivables setup, its own approval rules, its own data access assignments. Twelve business units means twelve of everything to maintain.
Then what it buys: data segregation, so users of one business unit cannot see another's transactions; independent processing, meaning separate payment runs and separate close; and genuinely different operating rules where they differ.
Five decision questions. Do different groups need to be prevented from seeing each other's transactions? Do they pay suppliers on different terms, or from different banks? Do they close on different schedules? Is there a legal or regulatory requirement to separate? Will the same people process for all of them?
Fewer is better until a specific requirement forces more. Data segregation is the most common legitimate driver. "Different departments" is not — that is what cost centres are for, and you will be asked for a business unit per department at least once.
Two scenarios are worked through live: a single-country wholesaler with three brands, and a two-country group with shared services.