Couchbase Lite - App backgrounding best practices

A common use case/issue is working with the possibility of an app being backgrounded/closed etc. and how this affects replication. At a very high level, the answer here is that we're at the mercy of the OS and whatever restrictions or requirements it imposes.

That said, given that this has such potential to impact an app's use of Couchbase Lite, it would be good to call out the behaviour on different platforms in different cases, and potential options. I don't expect that anything here would be unique to Couchbase Lite, but as it's so closely related there's an argument that branching out into more generic Android/iOS/.NET information would greatly improve the documentation.