A big component that works against an adequate crawlspace climate as well as the home's foundation is the presence of water. We don't experience it often in Southern California, but other parts of the USA experience water intrusion into the crawlspace of homes at a very high level.
Installing a vapor barrier, sump pump system, and dehumidifier system are the best items to utilize to minimize excessive moisture and water in a crawlspace. On top of these item being installed within the crawlspace, adding necessary draining around the perimeter of the home will minimize the amount of water that can enter into a crawlspace.
Water and moisture beneath your home in the crawlspace is bad. It can lead to mold and poor breathing environment as the air from the crawlspace makes it way up into your home and through your vents. Moisture also has a way of deteriorating concrete at a faster rate when it is introduced or in constant contact with it. Efflorescence is a bi-product of water being in contact with the concrete for a prolonged period of time. This is the white flaky dust that occurs on the concrete when it has dried out to a certain level.
Water intrusion is something that we must control to keep our home's and our health up. Being in a home that has excessive water intrusion will structurally compromise the home as well as compromising you and your family's health.