I know one can just have multiple LastPass entries.
But for sites hosted internally within your own network, it might be handy to formally be able to declare multiple URLs for the same LastPass entry. One for the internal URL/IP Address, and another for the external URL/IP Address.
Where this would come in the handiest, I'm thinking, is during the Security Score check. Alternate URLs would eliminate duplicate LastPass entries, and reduce the number of flagged password duplicates (or triplicates, or ...).
A second really handy use-case would be the legitimate scenarios where a company has a shared password (utilizing SSO perhaps) across disparate sites with multiple URLs. This isn't super common with me, but it has caused me to build out duplicate passwords when it wasn't strictly necessary to list them that way within LastPass.