As with other principles of gardening, the gardener does not want there to be competition for nutrients, either on the level of the garden predators or the level of the plants themselves. Planting such that this competition for nutrition is minimized will allow a garden to grow and thrive and maintain as good a balance of beauty and order as possible. Some plants discourage the colonization of some animals. Research must be done so that the garden runs as smoothly as possible.
Also, especially in the case of butterflies, the adult is beneficial and the larvae are harmful. Especially in the case of the organic garden, some kind of imperfect compromise may have to be reached if one is to enjoy butterflies in the garden and plant accordingly.