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.
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.