Raw land is nothing more than basic earth. Land on its own can be improved to add value, and it can be leased or rented to be used by a billboard marketing company or cell phone carrier company for their towers to create cash-flow. Land can also be subdivided and sold for profit. Some investors choose to buy raw land with hopes that someday the land will become much more valuable due to external developments like the construction of a freeway or from a development being built nearby.
A few years ago, a personal friend of mine heard through the grapevine that Yale University was considering expanding to a new location. He found a parcel of land in that area and bought it for a great price. He held onto it for just over 1 year and then sold it to Yale for triple what he paid for it.