One-Part or Two-Part Spacecraft?

[Sharpy]

My rule is "Not taking too much junk on the long haul."

My rover for circumnavigating Duna was just that, a rover with all it needed. OTOH the rover for Minmus, which was meant to visit just a couple biomes (still visited them all) had everything it needed to enter Minmus orbit.

No interplanetary mission carries Kerbin reentry stuff (unless their target reentry stuff can be reused for Kerbin). The reentry vehicle always waits in LKO.

The Eeloo mission currently is taking the idea to extreme and twisting it. It has no fuel for return. It has no ISRU on board. But it has a manufacturing workshop and a base deployment essentials, and two nuclear reactors. It's not hauling stuff it won't need in either direction - it will manufacture all that's needed for return on site.