Prevent Moisture from entering your basement, Crawlspace and eventually causing Mold.
The foundation can be coated before they backfill with dirt. This will ensure the block will not let water / moisture seep through. If they already backfilled, it can still be coated, but wont be as easy as doing it from the start.
The crawl Space will attract moisture because of the cool dark spaces. Having the crawl space lined with plastic like the photos is generally how it’s done.