Tree-climbing practice focuses on "gathering" Chakra, using this gathering mechanism to allow the soles of one's feet to adhere to trees. Water-surface walking practice focuses on "releasing" Chakra, using this release to expand the surface area of contact with the water, increasing buoyancy so that one can stand upon the water's surface.
Though these concepts of "gathering" and "releasing" might seem unremarkable at first glance, they dramatically improve Chakra control. When combined with hand seals, one can theoretically master all Ninjutsu in this world. Of course, actual mastery still depends on Chakra nature affinities and additional requirements.
Uchiha Chi even felt that if one could push this "gathering" and "releasing" to their absolute extremes, one could grasp the very essence of Chakra. Naturally, this was merely a gut feeling—not even a theory, let alone a method—yet it did nothing to deter him from striving toward that goal.
Chapter 18