  The modeling of Li-Paczy\'{n}ski macronova/kilonova signals gives reasonable
estimate on the neutron-rich material ejected during the neutron star mergers.
Usually the accretion disk is more massive than the macronova ejecta, with
which the efficiencies of converting the disk mass into prompt emission of
three merger-driven GRBs can hence be directly constrained. Supposing the
macronovae/kilonovae associated with GRB 050709, GRB 060614 and GRB 130603B
arose from radioactive decay of the r-process material, the upper limit on
energy conversion efficiencies are found to be as low as $\sim
10^{-6}-10^{-4}$. Moreover, for all three events, neutrino annihilation is
likely powerful enough to account for the brief gamma-ray flashes. Neutrino
annihilation can also explain the "extended" emission lasting $\sim 100$ s in
GRB 050709, but does not work for the one in GRB 060614. These progresses
demonstrate that the macronova can serve as a novel probe of the central engine
activity.
