I am working on a spaceship design tool. And one problem I run across is that to economically operate, starships either need a hell of a lot of propellent, or the need to travel for weeks at at time. The problem with the slow boat approach is that the more people you have on board, the more sewage and trash pile up, meaning you start to need a dedicated "dump" built into the ship to store all of that nastiness.

On short flights with small crews the effect is negligible.