At its best, management intensive grazing mimics the ecology of a native prairie.  Quick bursts of heavy grazing result in pastures that are extremely diverse, often hosting up to 30 plant species.  Trees and shrubs don't have a chance to get a foothold the way they do in pastures that are continuously grazing with low numbers of animals, and the grasses and legumes produce a lot more leaves than they do when you're grazing continuously with lots of animals.  From an animal's point of view, the result is much higher quality forage and a lot more of it.

The image above shows how putting animals on your pasture only during the optimal grazing window produces the maximum amount of forage of the highest nutritional value.  The far left side of the graph shows what happens if grass is grazed nearly down to the ground --- at first, the plant grows very slowly because it has to use up stored energy in its roots to create new leaves.  As the leaf area becomes large enough to grab energy straight from the sun, the plant grows faster and faster.  But then the plant decides to flower, so it slows down leafy growth in order to push some energy toward blooming.  After a certain point, the plant isn't making any extra leaves at all because it has gone to seed.

To get the most from your pasture, you must keep your plants between the two stages marked with red lines in the diagram.  You never graze the pasture so low that the grasses have to pull too much energy from their roots and you never let them get so tall that they start to bloom.  For poultry, sheep, goats, and pigs, you should let the grass grow until it's 3 to 4 inches tall, then graze it down to 1 to 2 inches tall before repeating the cycle.

Bill Murphy has experimented with various methods of renovating poor pastures, and has discovered that well-timed bouts of grazing of the sort outlined above are just as effective as costly campaigns of killing the existing sod and seeding new pastures, overseeding with clover, or alternating pastures with row crops.  Keeping the nitrogen content of the soil down and the grass grazed low enough favors clovers, and they seem to spring up on their own to fill in more and more of the pasture sward every year.  That means richer and richer forage for your grazing animals to eat.