The primary concern in collapsing all controllers to a single cluster located in central Europe is that some channels may not be available consistently across the organization. This is because regulatory domain restrictions (such as allowed Wi-Fi channels and power levels) differ by country, and a centrally located controller cluster will enforce the regulatory domain of its own region (Europe), which may restrict or disallow channels that are needed in other regions where the organization operates (such as the US or Asia).
https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/86/b_Cisco_Wireless_LAN_ Controller_Configuration_Best_Practices.html