The point is simple. The delta-V per rocket stage is governed by the Tsiolkovsky equation: dv = Isp * g0 * ln(m_start/m_end) So, if m_end goes to zero, you g

The point is simple. The delta-V per rocket stage is governed by the Tsiolkovsky equation: dv = Isp * g0 * ln(m_start/m_end) So, if m_end goes to zero, you get a significant dv gain. It has absolutely nothing to do with the "efficiency" of returning a stage or not.