Recommendation: After you apply a patch within the same release codeline, Oracle recommends as a best practice that you export the data from your databases, clear the data from the databases, and then reload the data.
For customers with a handful of databases this probably isn't a big deal. But for shops with 500 databases covering many terabytes of disk this could be a huge task literally requiring months of effort.
My best guess is that they've changed the format of files being written to disk but I'm not really sure. Also note that it's a recommendation. But not following those can come back to bite you when you're trying to fix a production down issue in the middle of the night and the level 1 support technician asks very casually, "did you do an export, clear and load after you patched this server?" You've been warned.