I agree for people with unstable connection it should be time saver, but I wouldn't say it is a first case scenario. Do we know how many devs have problem with connection?
Any way a simple scenario is the best way to encourige people to build it and provide some options to consider if something failed.
If there are problems with downloading all deps then there should be specific errors, that leads to using local repo, until then it is not a first option to consider IMO. But first simple way to build is not even mentioned here.