  Accreting black holes are unique tools to understand the physics under
extreme gravity. While black hole X-ray binaries differ vastly in mass from
AGN, their accretion and ejection flows are assumed to be essentially similar.
Black hole X-ray binaries or microquasars are, however, quasars for the
impatient as variability timescales scale directly with mass. State changes,
i.e., strong variations in emission properties, in black hole X-ray binaries
can happen within hours and whole outburst cycles within months to years. But
our understanding of the drivers of such changes and the contributions of
individual accretion and ejection components to the overall emission is still
lacking. Here, I highlight some of the INTEGRAL's unique contributions to the
understanding of black hole X-ray binaries through its coverage of the energies
above the spectral cutoff, its long uninterrupted monitoring observations and
the measurements of hard X-ray / soft $\gamma$-ray polarization.
