is there some general rule of thumb that advises when it's
appropriate to create multiple channels within a single network, and
when it's appropriate to simply create entirely distinct fabric
networks?

clearly(?), one of the driving rationales behind multiple channels
is the efficiency in sharing commonality across the channels, such as
when many of the same orgs are involved, or some of the same
chaincode, and so on. but does there come a point where there's just
not enough commonality to justify multiple channels in a single
network?

my analogy is someone saying, "hey, let's check all this content
into a git repository," while someone else observes, "well, all that
content really is two fairly disparate code bases, i'm thinking it
makes more sense to create two independent repositories."

is there some analogy with fabric in here somewhere?

rday