  Accurate quasar classifications and redshift measurements are increasingly
important to precision cosmology experiments. Broad absorption line (BAL)
features are present in 15-20\% of all quasars, and these features can
introduce systematic redshift errors, and in extreme cases produce
misclassifications. We quantitatively investigate the impact of BAL features on
quasar classifications and redshift measurements with synthetic spectra that
were designed to match observations by the Dark Energy Spectroscopic Instrument
(DESI) survey. Over the course of five years, DESI aims to measure spectra for
40 million galaxies and quasars, including nearly three million quasars. Our
synthetic quasar spectra match the signal-to-noise ratio and redshift
distributions of the first year of DESI observations, and include the same
synthetic quasar spectra both with and without BAL features. We demonstrate
that masking the locations of the BAL features decreases the redshift errors by
about 1\% and reduces the number of catastrophic redshift errors by about 80\%.
We conclude that identifying and masking BAL troughs should be a standard part
of the redshift determination step for DESI and other large-scale spectroscopic
surveys of quasars.
