🧱 It's time for MC Next Business Units Architecture! 

TL;DR: Default to a single BU until a hard requirement forces the split: 

https://mateuszdabrowski.pl/docs/salesforce/marketing-cloud/config/business-units/

The decision tree in the article has an "Are you sure?" step for a reason... New Business Units work differently to what you know from the good old @* Marketing Cloud Engagement *

On @* Marketing Cloud Growth & Advanced * a Business Unit is a thin marketing layer over exactly one Data 360 Data Space. The Data Space is the real wall - no hierarchy, no per-BU login, everything you can access in one view, with a badge telling you where you are. 

Three things to know before you click create: 

🔵 It's forever. A Business Unit can't be deleted, deactivation is permanent, and the Data Space it consumed can never serve another one. You get 2 included with Advanced Edition, and can pay your way up to 150 total since Summer '26. 

🟠 Splitting splits everything (duh!). Segments, flows, content and reporting all partition with the Data Space - cross-BU reuse means deployed copies (Data Kits, Common Assets), multiplied processing, and no consent sync! 

🔴 Governance has one blind spot for the recommended Single BU approach. Data 360 row-level visibility control holds almost everywhere - except segment and Calculated Insight runs. Region filters on segments stay manual. 

In the article, you will find a trade-off matrix (Data, Segments, Consent, Domains, Licensing, and more), architecture patterns, and the Global BU duplication tax.