It is very important if you are buying/selling a home or have owned your home for some time to have the crawl space inspected. A key component of a house is the foundation it is built upon.
I have seen many nice houses built on a few rocks or chunks of firewood. Consequently the floors were out of level. This doesn’t necessarily mean that you shouldn’t purchase the house but you should know the type of foundation as it can be a costly repair.
Another couple of reasons that the home inspector should if possible inspect the crawl space is to make sure insulation is properly installed, vapor barrier in place and integrity of the floor Joice and sill plate. Just last fall I inspected a home that in one area had rotten sill and rim plate. This was due to a deck added on with out proper drip edge installed.