Insulating and "conditioning" your crawl space will increase the overall temperature of the space and make the floors above it more comfortable. The goal is to bring the crawl space "closer" to the inside. Crawlspaces can be converted from an unconditioned to a conditioned space which includes sealing off any vents to the outside, insulating the foundation walls, and installing a vapor barrier on top of the dirt floor.  Radon gas is known to exist in the soil here in CO and a properly installed vapor barrier can minimize the potential for any transmission of Radon from the soil as well as keeping out dirt, dust, moisture, and bugs!