  The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy
(SCALES) is a $2-5~\mu$m, high-contrast integral field spectrograph (IFS)
currently being built for Keck Observatory. With both low ($R\lesssim250$) and
medium ($R\sim3500-7000$) spectral resolution IFS modes, SCALES will detect and
characterize significantly colder exoplanets than those accessible with
near-infrared ($\sim1-2~\mu$m) high-contrast spectrographs. This will lead to
new progress in exoplanet atmospheric studies, including detailed
characterization of benchmark systems that will advance the state of the art of
atmospheric modeling. SCALES' unique modes, while designed specifically for
direct exoplanet characterization, will enable a broader range of novel
(exo)planetary observations as well as galactic and extragalactic studies. Here
we present the science cases that drive the design of SCALES. We describe an
end-to-end instrument simulator that we use to track requirements, and show
simulations of expected science yields for each driving science case. We
conclude with a discussion of preparations for early science when the
instrument sees first light in $\sim2025$.
