Scopes should be removed when a subnet is no longer in use or when you need to renumber your network to use a different IP address range.
You must deactivate a scope before removing it. This enables clients using the scope to renew their lease in a different scope. Otherwise, clients lose their leases and possibly network access (if they cannot auto-configure).
To ensure that all clients migrate smoothly to a new scope, you should deactivate the old scope for at least half of the lease time, or until you have manually renewed all clients, to remove them from the inactive scope. For more information about deactivating scopes, see Windows 2000 Server Help.