[rbanffy]

It's smart to launch supplies in low-energy orbits so as to increase the mass you can get to Mars for the same fuel budget. Humans have to transit quickly between the planets, but supplies can handle a much longer trip on a much less comfortable spacecraft and, to be there for the humans, they'll have to launch much earlier.

And yes, no sane human being would consider launching to Mars before a return vehicle is already settled at the destination and ready to take off. The return vehicle and its backup. And the habitats, supplies and everything else.