  Hubble Space Telescope SNAPshot surveys of 86 X-ray selected galaxy clusters
at $0.3 < z < 0.5$ from the MACS sample have proven invaluable for the
exploration of a wide range of astronomical research topics. We here present an
overview of the four MACS SNAPshot surveys conducted from Cycle 14 to Cycle 20
as part of a long-term effort aimed at identifying exceptional cluster targets
for in-depth follow up by the extragalactic community. We also release
redshifts and X-ray luminosities of all clusters observed as part of this
initiative. To illustrate the power of SNAPshot observations of MACS clusters,
we explore several aspects of galaxy evolution illuminated by the images
obtained for these programmes. We confirm the high lensing efficiency of X-ray
selected clusters at $z>0.3$. Examining the evolution of the slope of the
cluster red sequence, we observe at best a slight decrease with redshift,
indicating minimal age contribution since $z\sim 1$. Congruent to previous
studies' findings, we note that the two BCGs which are significantly bluer
($\geq 5\sigma$) than their clusters' red sequences reside in relaxed clusters
and exhibit pronounced internal structure. Thanks to our targets' high X-ray
luminosity, the subset of our sample observed with Chandra adds valuable
leverage to the X-ray luminosity--optical richness relation, which, albeit with
substantial scatter, is now clearly established from groups to extremely
massive clusters of galaxies. We conclude that SNAPshot observations of MACS
clusters stand to continue to play a vital pathfinder role for astrophysical
investigations across the entire electromagnetic spectrum.
