When collapsing all controllers to a single cluster in a central location, one must consider the availability of channels across different regions. Regulatory domains vary globally, and certain channels allowed in Europe may not be available or legal in other parts of the world. This can affect the consistency of wireless coverage and performance.
https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/86/b_Cisco_Wireless_LAN_Controller_Configuration_Best_Practices.html