There are benefits to hauling manure.
Manure aerates the soil and helps it absorb and cling to water.
Nutrients from synthetic fertilizers are used up or washed out of the soil by the end of a season, but benefits from each application of manure continue for years. When we talk about manure, we mean animal excrement plus bedding. The amount of nourishment manure supplies to a plant the first season depends on the ratio of bedding to excrement. More bedding means less nourishment to plants the first season, but a greater residual effect for subsequent seasons. The heat comes from the burst of microbial activity stimulated by these manures' relatively high concentrations of nitrogen and low concentrations of water.