Shared posts can be filtered by taxonomy terms. Filters can be set to either inclusive or exclusive behavior. The default is exclusive.
Exclusive Filtering
If the setting “Check [taxonomy terms] will be shared”, then is not checked, then each term checked will exclude posts with that term from being shared. The inclusion of other terms does not matter; the presence of the excluded term will prevent sharing.
Inclusive Filtering
If the setting “Check [taxonomy terms] will be shared” is checked, then posts will only be shared if they include the checked term. The inclusion of other terms does not matter; the presence of the included term means that this post should be shared.