All plants “want” to produce seeds in order to spread their genetic lineage. In some leafy vegetable varieties, heat, day length, or other stress can cause the plant to set seed prematurely. Bolting refers to the process of the plant suddenly ending its vegetative (leafy) growth, and focusing all its energy on flowering and setting seed. It is sometimes called “running to seed.” Once this process begins, the leaves may become tough or bitter, or otherwise unappealing. Bolting is a problem particularly for lettuce, spinach, and some other leafy plants (arugula, sorrel, cilantro, cress…), because they grow best in cool soil. Bolting also occurs in beets, radishes, celery, onions, and many others. Once the soil warms up in summer, it’s smart to switch to crops that prefer warm soil. It is recommended that dill is direct sown because the stress from transplanting may cause it to bolt.
Because bolted plants are no longer useful to the grower, it may be a good choice to remove them so they don’t take up valuable space in the row — and also to prevent them from self-sowing. If a plant like kale or lettuce is allowed to go all the way to seed, it may become a real nuisance as a weed in the garden.
However, it can be educational and insightful to watch how particular plants flower, and many vegetable and herb flowers are attractive, and even edible. Many Brassicas, including radishes and kale produce seed pods that are edible as well. Just be prepared to remove the plants before the shed seeds everywhere.