Gardeners Sometimes Plant Clover Between Productive Growing Seasons

Gardeners sometimes plant clover between productive growing seasons. Why would this practice be beneficial?

A) Several types of nitrogen-fixing bacteria form a symbiotic relationship with the roots of clover. This would increase the amount of nitrogen in the soil available for subsequent seasons of other plants' growth.
B) Clover is consumed by a number of animals. This would encourage the animals to feed/graze on the areas, leaving behind nitrogen-rich manure (feces) that would act as a natural fertilizer for subsequent seasons of other plants' growth.
C) Clover is a unique plant that is capable of atmospheric nitrogen-fixation (pulling nitrogen directly out of the air and turning it into ammonia or amino acids) . This directly provides nitrogen compounds for the soil for subsequent seasons of other plants' growth.
D) The beneficial effect is more for water retention and elimination of soil erosion in between growing seasons than for any nutrient value. It has nothing to do with nitrogen compounds in the soil.
E) Several types of oxygen-fixing bacteria form a symbiotic relationship with the roots of clover. This would increase the amount of oxygen in the soil available for subsequent seasons of other plants' growth.