Creating a replicated bucket protects your data against region failure and makes it accessible during outage. So replicated buckets is a way to reach higher availability, should you have those requirements.
Example:
You have created a replicated bucket and se-central-1 experiences network outage.
After re-pointing your application or tool to se-north-1, you can continue to access your data.
Once se-central-1 is back in operational state, replication engine will make sure any changes to your data is reflected to se-central-1, in this example.