A patch conflict is rarely limited to two patch IDs. In a long-lived Oracle Home, an installed one-off may be the base for an overlay, and another patch may depend on that overlay. Replacing the first patch can therefore create a chain of rollback dependencies that OPatch must process in the correct order.
The -optimize option is designed for this situation. When a supported OPatch version detects that an incoming patch conflicts with an installed patch, it can calculate the dependency-aware sequence, roll back the conflicting patch and its installed dependents recursively, and then continue with the incoming patch.