Once your payload exceeds the SSTO capability of a single BFS launch, you save effort by doing a two-stage launch. The two-stage launch is more complex and difficult, but the added capacity is far greater.
For intuition, consider moving to a new house. What’s better, renting a tiny car with room for one suitcase, or renting a big truck? The car is cheaper and easier to drive, but unless all of your stuff fits in one suitcase, the truck is going to be much cheaper and easier for this task.
For intuition, consider moving to a new house. What’s better, renting a tiny car with room for one suitcase, or renting a big truck? The car is cheaper and easier to drive, but unless all of your stuff fits in one suitcase, the truck is going to be much cheaper and easier for this task.