The Moon has fuel and manufacturing opportunities. With current technology the Moon travel costs can be cut with the advent of lunar space elevators. The Moon can provide nuclear power to enable mission to not only Mars, but ideally Titan. Solar panels can be manufactured for local power, geothermal energy opportunities are present, and much more.
Titan has ethane/methane fuel, water, plus local access to 60+ moons with a big gravity well. Saturn's orbit is powerful and can propel fuel transports between the bodies. The Moon is a better rendezvous point than Earth and has a similar gravity profile as Titan, even similar temperature conditions in certain places. Our Moon and Titan are not so different. The equipment used on these moons such as spacecraft, life-support systems, fuel containment, and artificial gravity systems are equally compatible. Shipping methane to the Moon and oxygen back is a sustainable way of exploring the outer solar system and beyond.