Oracle patchsets used to be simple - they were bugfixes only; no additional functionalities were added. Oracle added stuff quietly in 10.2.0.4 patchset (the workload capture); but that was part of a new functionality anyway.
The 18.104.22.168 patchset changed all the rules. Several new functionalities were added to the patchsets. Several functionalities have been added to RACOne. Unfortunately they didn't make it to the manuals. Some of them I discovered only recently. If you have been using RACOne, or considering it, you will be delighted to know these.