The mystery of "only master on the bus".

Hi S7 fetishists,

does anyone have a clue to what the setting "PC/PG is only master on the bus" or "panel is only master on the bus" REALLY does ?

A recent FAQ by Siemens suggested that both PC and HMI panel choose this setting when downloading applications. I find it strange, as then there will be 3 MPI masters (PLC + PC + HMI), where 2 claim to be "only master".
Can it be that this setting really does something completely different than what the name implies ? (Something which is not unheard of when it comes to S7 lingo).

It has to do with token passing- if I told you more I would have to
kill you.

did you solve this mystery ?!

If you do NOT set the "Only master on bus", a device that is master will check the bus settings before attempting to connect to the bus. If there is then already a master, and this master uses different bus settings, the connection attempt is stopped.

If you DO set the "Only master on bus", the device that is master will NOT check the bus settings before attempting to connect to the bus. If there is then already a master, and this master uses different bus settings, the new master will try to connect, possibly causing a bus failure for the other master.

In other words, I see no reason to select the "Only master on bus". Only advantage would be that the connection would be slighly faster, at the risk of causing bus failures.