It is optional to apply a patch with downtime, but it is more fast and it requires less system resources as it seems.. On the other hand; with downtime mode; you 'll have an increased system downtime..
As you know, in EBS 12.2; we dont have a maintanence mode anymore .. That's why; to apply a patch with downtime , we only need to stop our application tier services..
What we need to do is ;
Step 1) Source our run environment.
Step 2) Stop our application services
Step 3) adop phase=apply apply_mode=downtime patches=PATCH_NUMBER
With apply_mode=downtime ; adop directly applies the patch .. No patching cycles...
But we need to face the facts;
As Oracle states;
There are some examples for these kind of situations;
Oracle suggests and supports this downtime apply mode for the fresh installations, upgrades and for some specific product upgrades at the moment;
When the system is started to be used by the users ; in other words when we put data into it/ when we start the business processes, we need to apply our patches online unless otherwise started in the Readme or corresponding note.
To be able to use dowtime mode; you need to upgrade AD-TXK Delta 5, or you need to upgrade to 12.2.4.. Note that you need to upgrade your AD-TXK DELTA 5 prior to 12.2.4 upgrade anyways
When you apply AD TXK Delta 5 as a prereq for 12.2.4, you may even use downtime mode during the application of your 12.2.4 upgrade patch.
For AD-TXK Delta 5 upgrade >
Applying the Latest AD and TXK Release Update Packs to Oracle E-Business Suite Release 12.2 (Doc ID 1617461.1)
For 12.2.4 Upgrade >
Oracle E-Business Suite Release 12.2.4 Readme (Doc ID 1617458.1)