Удивительно, но я то ли плохо прочитал, то ли пропустил замечательную статью Bezanson J., Bolewski J., Chen J.
Fast Flexible Function Dispatch in Julia. ArXiv:1808.03370 [Cs], 2018 (
http://arxiv.org/pdf/1808.03370.pdf). Пока лучшее из виденных коротких объяснений Function Dispatch.
Действительно объясняет вывод: We have describe the design and implementation of Julia’s dynamic dispatch mechanism to supporting high-level technical computing programs that also have good performance. In Julia, the combination of dynamic multiple dispatch and on-demand method specialization allows users to write generic code. By providing a uniform language for technical computing programs, Julia provides flexibility and ease of reasoning without requiring the programmer to give up performance.