Hello MIchael
The MST revision number is one of the attributes used to identify a unique MST region. It is a construct that can be used by administrators to ensure that the configuration is the same on all switches in the region.
The idea is that every time you make a change to the MST configuration on a switch, you increment the revision number by one on that switch. In order to get the rest of the topology to sync up to that change, you must go into each switch in the region, and increment the revision number by one. This is a manual process and can be cumbersome especially if you have many switches.
My personal opinion (and one that others share as well) is that this is an outdated way of ensuring conformity across all MST switches. In practice, the revision number is maintained the same simply because it is inefficient to use this method of ensuring configurations are the same throughout the region.
I hope this has been helpful!
Laz