Why Lookup on Account to Global Address?
An Account can reference a single default Global Address via a lookup field, allowing multiple Accounts to share the same address.
This is more efficient than the reverse (lookup on Global Address to Account), as Global Address is the parent in this relationship.
Avoiding Master-Detail:
Lookup relationships provide flexibility in this use case since Accounts and Global Addresses have independent lifecycles.
Example:Create a custom lookup field on Account referencing the Global Address object.