What are the benefits of having a heavy lift launch vehicle, compared to using several smaller launches and assemble the spacecraft in orbit?
There must've been more than a hundred successful dockings (and berthings) in space, including in Lunar orbit, and especially for building and supplying the ISS. The only docking failure I know of is the Progress M-34 to MIR in 1997 (they seem to have shut down the radar and looked out of the window holding a laser range finder...) and even then they didn't lose the mission. So docking seems mature and doesn't add substantial risk.
How important would the costs of docking systems and fuel for maneuvering in orbit be? Is the logistics of timing multiple launches a problem? Could we use today's small launchers to spend several years to build a Mars spaceship in LEO, like we did with the ISS, and fuel it and send it on its way whenever it is ready? Do economies of scale benefit large launchers for large missions, or is it the other way around because small launchers can be mass manufactured? What are the key issues with multiple small launches versus a single big one?