Think of seeds as plant babies. If all seeds fell straight from the plant to the ground, the seedlings would be competing with each other, and with the parent plant, for the same water, sunlight, and nutrients. Few, if any, seedlings could survive beneath the parent plant. Seed dispersal is one way to avoid this type of competition. Some plants take advantage of rivers, floods, rain, or ocean currents to disperse their seeds.
Some species even have a waterproof husk, such as the coconut.
Some seeds, like burrs, have hooks that catch in an animal's fur or on our clothing. Other seeds are surrounded with tasty fruit. In some species, the animal eats the fruit, and the seed is left behind to germinate. In others, the fruit is eaten whole and the seeds are excreted in the animal's droppings. Many seeds are dispersed by animals such as squirrels, or jays, that bury them for the winter, but then forget to eat them, giving the seeds a chance to sprout.