If EBS in R12.1 or R12.2 in shared file system, patching down time will be reduced.
Please go through the below blog , you can understand the advantages
Can you share more details about your environment.
How many servers . you have ?
Database and apps running on different machines
Do you have multiple apps servers ?
Its easier to keep everything consistent and in synch with shared file system.
We use NFS for our file system and it makes it easy for backups and cloning.
In my opinion, the only reason you wouldn't want to use shared file system is if you have a very specific reason to not share the file system. Its difficult to think of reasons why... maybe a server is in a DMZ or something...