What Is the Function of an Apical Bud?

Apical buds produce auxin, which is distributed throughout the plant through the phloem. Auxin prevents lateral buds from growing so that the plant can use all available energy on growing the apical bud. When a plant grows tall, it is able to reach sunlight so that it can undergo photosynthesis. According to Wikipedia, apical dominance is most likely adaptive because if a plant is able to out compete others in the vicinity, it has higher fitness.