Why enable maintenance mode

I received email from one of my readers about maintenance mode (oracle application).

Q1: why we need to enable maintenance mode when we are shut down all the application during patching?

A1:  maintenance mode ensure optimal performance and reduce downtime during patching sessions, Autopatch required that enable maintenance mode when apply a patch. 

enabling maintenance mode shut down the workflow business events and set up function security so that oracle functions are unavailable to users.

Q2: Can we apply patch without enable maintenance mode?

A2: Yes, we can apply patch without enable maintenance mode but it is not recommended.

Q3: How to apply patch without enable maintenance mode?

A3: use the following syntax

adpatch options=hotpatch