Comment by ggreer

Rocket engines can’t throttle down very much. Raptor can go down to 40% of its rated thrust, which for V3 would be 100 tons. The ship’s mass is maybe 150 tons with remaining propellant at the start of the landing burn, and probably around 100 tons at the end of the burn. Even at the lowest throttle, three engines would give it a thrust to weight ratio of 2, making hovering impossible and a suicide burn tricky. Two engines gives them redundancy, roll control, and a lower thrust to weight ratio to help with landing precision.

I’m surprised they went down to one engine at the end, because that means they lose most of their roll control. The only way to roll with one engine is to use the cold gas thrusters, which aren’t nearly as powerful.