I've seen it used by a few people. It sure would be nice to know what the number means! Is that total number of divisions? I don't think so. Is it a weight? So that if you have a low figure (relative to the other garrison figures) then more units will be sent over seas for garrison duty?
I don't know any way to specifically send troops to an allied province either. If the troops become expeditionary troops then the garrison values (province priority) do seem to be used.
- Mithel