  With the advent of more sensitive all-sky instruments, the transient Universe
is being probed in greater depth than ever before. Taking advantage of
available resources, we have established a comprehensive database of black hole
(and black hole candidate) X-ray binary (BHXB) activity between 1996 and 2015
as revealed by all-sky instruments, scanning surveys, and select narrow-field
X-ray instruments aboard the INTErnational Gamma-Ray Astrophysics Laboratory
(INTEGRAL), Monitor of All-Sky X-ray Image (MAXI), Rossi X-ray Timing Explorer
(RXTE), and Swift telescopes; the Whole-sky Alberta Time-resolved Comprehensive
black-Hole Database Of the Galaxy or WATCHDOG. Over the past two decades, we
have detected 132 transient outbursts, tracked and classified behavior
occurring in 47 transient and 10 persistently accreting BHs, and performed a
statistical study on a number of outburst properties across the Galactic
population. We find that outbursts undergone by BHXBs that do not reach the
thermally dominant accretion state make up a substantial fraction ($\sim$ 40%)
of the Galactic transient BHXB outburst sample over the past $\sim20$ years.
Our findings suggest that this "hard-only" behavior, observed in transient and
persistently accreting BHXBs, is neither a rare nor recent phenomenon and may
be indicative of an underlying physical process, relatively common among binary
BHs, involving the mass-transfer rate onto the BH remaining at a low level
rather than increasing as the outburst evolves. We discuss how the larger
number of these "hard-only" outbursts and detected outbursts in general have
significant implications for both the luminosity function and mass-transfer
history of the Galactic BHXB population.
