In addition to Oban’s internal use, the notifier is available for use by other application code. All it would take is serializing a large enough map.
The most common Oban driven examples are for oban_met when it hands off the current metrics between nodes or in oban_pro when using the Relay module.
There are many notification payloads, and they’re all kept as small as possible. No notification includes the entire job data. Insert triggers, which are a very frequent notification if you don’t disable them, only include the queue name.