Important Note:
Follow this knowledge base if you are changing the custom base URL in a federated repository environment.
The Custom Base URL is mainly used for telling the application what DNS address it's running on, mainly for specific package clients and connections with other instances that require a call to the DNS entry (so it can relay this information, as otherwise apart from some headers it doesn't really know what DNS it's running on).
Follow this knowledge base if you are changing the custom base URL in a federated repository environment.
The Custom Base URL is mainly used for telling the application what DNS address it's running on, mainly for specific package clients and connections with other instances that require a call to the DNS entry (so it can relay this information, as otherwise apart from some headers it doesn't really know what DNS it's running on).