This was done for a few reasons...
1) Duh, it looks bad-ass! :)
2) Keeps the interior a bit cooler in the summer
3) darker inside for daytime naps (3 year old)
4) Blocks UV rays, my wife had Stage 3 Melanoma 10 years ago... want to keep it that way.
5) keeps the curtains looking new, no fade from the UV rays
6) Needed to hide the new interior wall - about a foot of the rear window will be blocked by a new wall inside for the bathroom. (Port side)