The big difference is that, on Earth, you need to be operating continuously over the entire distance, thanks to friction, traffic, weather, and other environmental hazards.
In space, you just set your trajectory and then go to sleep until you get to your destination. We do it all the time when sending probes around the system. There's basically nothing to hit - even when sending probes through the asteroid belt beyond Mars, the densest debris field in the solar system outside of Saturn's rings, and almost entirely unmapped, we just don't worry about it - there's so little material scattered across such a large space that the odds of an unintentional collision are vanishingly close to zero. Even radiation is roughly constant, aside from solar flares. For non-living goods either it can pretty much handle it, or it can't.
The result being that it doesn't actually make much difference whether you're sending a vessel across the solar system or just leaving it in high orbit - the non-fuel costs and risks are roughly the same. And we've gotten good about building hardware that doesn't mind being left "asleep" for years while it coasts through space.
Yes, obviously, if you have people on board you need to keep life support, etc, running, and are dealing with cumulative radiation and risk exposure - but that doesn't actually change all that much once you reach your destination - be it in open space, the Moon, or Mars, you're completely dependent on life support, and are beyond Earth's magnetosphere - reaching your destination only cuts your radiation exposure by about half as the planet's mass shields one hemisphere (well, somewhat better than that on Mars thanks to the thin atmosphere and greater distance from the sun).
Basically, as long as you're living in a tin can outside Low Earth Orbit, it doesn't make a dramatic difference where you are in terms of risk or resource consumption, except for the cumulative biological damage due to microgravity. And while there's some reason to be hopeful, we don't actually know to what degree low gravity will negate those problems, though it seems likely that the higher gravity on Mars will reduce them further than on the Moon.
Yes, since you're being exposed to those risks regardless, it would be nice to not waste time just sitting around waiting to reach your destination, but if you're planning a multi-decade mission, a few months one way or the other isn't likely to make a huge amount of difference. Though, assuming you have inflatable or other "fast deployment" habitats that will offer substantially better radiation shielding than the ship, there's certainly a good argument to be made that you should get into them as soon as possible.