Clarify SPN configuration for web applications.

Added note about avoiding duplicate SPNs for the same service.

Author: HugoDurana

support/developer/webapps/iis/was-service-svchost-process-operation/understanding-identities.md

@@ -91,7 +91,8 @@ To understand application pool identities, you have to understand what an identi
     ```console
     setspn -a HTTP/MyWebAppZone.com Server1$
     ```
-
+    This situation results in duplicate SPNs for the same service (in this case, HTTP), where each server account has its own SPN — a configuration you should avoid.
+  
     To overcome this disadvantage, you can run the application under a custom Windows (domain) identity, and then set the SPN to only that specific domain account in the domain controller.
 
     Registering an SPN to a domain account: