What is the significance of spreading fruits and seeds?

Generally very large.
By spreading, even if not significantly (by throwing out an apple core, for example) any number of seeds, it is possible to restore the population of some trees, which in turn contribute to the release of oxygen, respectively, having a positive effect on the ecology and human health in general.
Some types of vegetation serve as homes and even natural feeders for animals, which are also important both in the ecological chain and in human life.