In warm humid areas they now air condition the encapsulated crawl spaces. As I recall it actually increases efficiency to condition the crawl space. I believe it has something to do with the temperature difference causing condensation.
In any case, encapsulation can make a big difference. My parents had their crawl space encapsulated when they bought their house. A few years later Terminex cut through all the side insulation to spray for termites. We realized what had happened when we started seeing cockroaches. Temperatures and humidity in the living areas increased. After they repaired the barrier the insect problem significantly decreased. We now see the occasional roach entering around drain pipes. Before the repair they had to run a dehumidifier inside the house almost constantly. Last summer they only used it a few days.
Last year my sister and her husband had to spend thousands of dollars repairing damage to their floor joists from mold. They had their crawl space encapsulated and the mold is now gone.
My parents spent about $5k getting their encapsulation redone. There were enough method and material improvements in the 5 years between projects that it was worthwhile to replace rather than repair the barrier. While encapsulation is expensive it protects your property investment and reduces utility expenses. It also can have significant health benefits.