Personally, I've never seen MO used. I always use SWM. They seem to work pretty much the same way. SWM and SO together or MO and Tieback together. SO is the same units as the PID output (0-100%), where TIEBACK in scaled using MAXTIE and MINTIE. I can't think of a single thing that I can do with the MO and TIEBACK pair that I can't do with the SWM and SO pair. There may be some additional code required for one vs the other but the same function can be achieved. That said, I see no reason to use both, so I'll stick with SWM.
Think of it as the A-B PID instruction's appendix. No one really knows why it's there, so they pretty much ignore it.
If anyone has an example where the MO and TIEBACK are neccessary, I'd love to see the code. I'd even be interested in seeing an example where it was just a cleaner design.