re: The Earth & LEO As Test Bed.
Which is what going to the Moon is all about.
Apollo 13 taught that lesson about backup systems. What other lessons do we need to learn?
Which is another advantage of the Moon. if something goes wrong and the astronauts die at least its close enough to get some good data feeds, even send an investigation mission out to recover the bodies and find out what went wrong.
Not as easy with Mars flights.