UPDATE_MODE clarification

[meyerovb]

Is setting UPDATE_MODE to continuous the same as running “docker exec -it nominatim sudo -u nominatim nominatim replication --project-dir /nominatim”?

The docs say ‘By default Nominatim is configured to update using the global minutely diffs.’ So is setting REPLICATION_URL required, or is it like just for pointing the environment to a closer mirror? Is there a downside to using the default instead of setting the url to a mirror?