In the (probably very) long term, a permanent Moon base capable of manufacturing and of growing food could be the key to human bases throughout the solar system.

Suppose you need to get from planet or moon X to planet or moon Y, using a rocket.

The usual way is to start at X and use the rocket to put yourself in an elliptical orbit that intersects both the orbits of X and Y. Then you coast in that orbit until it intersects Y's orbit, and use the rocket to put yourself in Y's orbit.

The nice thing about this approach is that it is speedy. If you only can carry enough fuel for limited use of the rocket, I think that this is the fastest way to go.

For a manned round trip mission, you have to take the speedy way, at least for much of the interesting parts of the solar system. Round trip to Jupiter, for example, would be several years at least.

If you do not care about speed there is a much cheaper way to get from X to Y. Interesting thing happen around various Lagrange points giving unstable orbits around them that can extend for vast distances away from the Lagrange point, and which take almost no energy to transfer to from an orbit that is close to the Lagrange point.

So you start in orbit around X, then move to an appropriately chosen X/Sun Lagrange point. This is not very expensive. At that Lagrange point, you nudge into one of those big unstable orbits. Eventually that orbit intersects and unstable orbit for a Y/Sun Lagrange point. A little nudge switches you to that, which eventually takes you to near a Y/Sun Lagrange point. There you can nudge again to get into a stable orbit, and from there it is cheap to get to Y.

But this is not fast. We're not talking nice straightforward elliptical orbits. The unstable orbit phase looks more like the path of one of those desktop tops where you have several magnets on a plate with another magnet on a rigid pendulum switching above it, and it looks like its motion is random. It can take a long time for it to get to one of the points where you can do the transfer to the other unstable orbit, and then that can meander a very long time before getting to the Y Lagrange point.

Depending on the particular X and Y, this can be anything from a few years to a few centuries.

This would be useless for transporting humans, but for long term transport of goods to support humans, it has a lot of potential.

Suppose you want to do a big base on Titan, say, and suppose it's 50 years to send things from around Earth to Titan via cheap unstable orbits. (I don't know how long it actually is...this is just for illustration).

What you can do is start sending regular supply packages to Titan this way. Send, say, one a month. It takes 50 years for the first one to actually arrive at Titan, and then after that you have one arriving per month.

When the supplies start arriving at Titan, then you send the manned mission via the normal fast orbits. Note that since you've got supplies at Titan already the manned mission only has to carry enough food and oxygen and water to last for the outbound trip itself. It does not need to carry anything for the stay on Titan, or for any return trip.

Ideally, what you want to do is as soon as you are technologically capable start using the slow but cheap unstable orbit system to start sending regular supplies to all of the places you think you might want to establish manned bases later. Over the next decades and centuries, as supplies start arriving at those places you can then send the manned missions to explore them, followed by the base building missions if you decide you do want bases there.

You could send them all from Earth, but doing this right would involve sending a whole lot of them over a very long time, and doing so from Earth would take a lot more energy than doing so from the Moon so it probably becomes a lot more feasible if you can make and launch the supply packages from the Moon.

Probably won't ever happen, though, because it requires long term planning on a scale that we no longer seem capable of.