Oracle Application-- Maintainance mode

Here is the main reason for maintenance mode and how it minimizes downtime:

There is a new Workflow feature called Cache Invalidation, which is built on the Business Events System. This feature generates Java cache invalidation messages for changes to seed data and, as a result, hampers the performance of FNDLOAD. As some patch sessions update a significant amount of seed data and also require running FNDLOAD in the background,
Having this feature enabled negatively impacts the performance of Auto Patch sessions. Maintenance mode shuts down the Workflow Business Events System.