The term 'deadheading' is defined as simply removing the dead or brown, sagging flowers on a perennial or annual plant. Everyone has done this at some point without realizing the benefits. Of course, it makes your plant look nicer with fresh, vibrant flowers. The science behind it is pretty simple and interesting. Any plant has one goal and one goal only; reproduce. Flowers are a plant's way of attracting insects like bees or moths or butterflies. This way the male parts of a flower which produce pollen, can be carried away to another flower where it will be 'pollenated." This ultimately produces a seedhead. A seed is the equivalent of an embryo. If we pull off the dead flower (ultimately the site of what will become the seed) the plant will never produce the seed. This triggers the plant to produce another flower in hopes of being pollinated again to produce a seed. If you neglect deadheading plants, it isn't a big deal. However, your plants will stop producing flowers and in some cases, it will begin to decline because again, it's life cycle is complete. Other plants simply remain in a vegetative state, meaning they continue to grow but just stay green. Iris is a good example of this. You can see above that neglecting to deadhead these Iris, a seed pod formed and unfortunately for these, flowering is done for the year. Otherwise they would have flowered all summer.