Never. This is a MMORPG, not a Mario game.

We all forgot why Jumping in a RPG is a bad thing, go back to Ultima 8. In summary, the jumping mechanics in RPG games are mostly a cosmetic thing, not functional. You can jump so you can pseudo-climb over inch small obstacles, where in V1.0 you couldn't jump at all and had to sometimes find really stupid long-way-arounds to climb up a path.

If the game had been designed as an action-RPG, jumping would be part of regular combat, which it isn't. At best, there's one mechanic in some of the mid-bosses that let you jump into a bubble.