  Spin induced precessional modulations of gravitational wave signals from
supermassive black hole binaries can improve the estimation of luminosity
distance to the source by space based gravitational wave missions like the
Laser Interferometer Space Antenna (LISA). We study how this impacts the ablity
of LISA to do cosmology, specifically, to measure the dark energy equation of
state (EOS) parameter $w$. Using the $\Lambda$CDM model of cosmology, we show
that observations of precessing binaries by LISA, combined with a redshift
measurement, can improve the determination of $w$ up to an order of magnitude
with respect to the non precessing case depending on the masses, mass ratio and
the redshift.
