I can tell you right now, first off, that movement during combat changes a very bland, removed feeling fight into something that actually feels dynamic and like real battle. This includes abilities that cause movement, jumping, or dodges (Tera did this very well recently).
So that said, I would say that I personally believe jumping should be useful in combat. I should be able to jump out of the way of directional attacks, as quite honestly just trotting out of the way feels extremely boring and almost defeats the purpose of even having the mechanic around. Utilizing interesting terrain in a fight, such as having a small chasm a player or group would need to jump across to avoid an enemy attack (such as a flood of water that might either damage or wash them away, but flows into that chasm and doesn't reach the other side) would also be an enjoyable experience.
I absolutely love jumping around terrain, so any sort of platforming-like exploration that might be possible I think would be extremely fun. I saw someone mention fall damage, and quite honestly I think dieing from falling is exceedingly stupid. While it's certainly realistic at large heights, I found myself enjoying a game where I wouldn't drop below 1 hp from a fall more fun to explore in than a game where I risked death if I took a wrong step on a mountain. That is unless you're trying to utilize the risk of falling off high things as a difficulty mechanic in a zone. If that is the case, I can understand death from a fall, but at the same time potentially having to go through an entire area again because you fell off at the end is pretty punishing as far as I'm concerned, and more importantly at least someone in your group doesn't have to potentially come raise you (furthermore if you fell off, hit 1hp, and landed on aggro, you'd be dead anyway).
Jumping could be utilized in fun ways for quests or events as well, if the 2.0 engine is capable of detecting a player jumping into moving objects (such as trying to jump and "catch" balloons or some such floating item, or items hanging from a tree like a fruit, etc). Even diving off something high into a river, pond, lake, etc for a random achievement, quest or event (cannonbaaaall). Being able to leap off of your chocobo to dismount rather than stop and just kind of... drop and be stupid for a second would be pretty cool as well.
I know this is a bit of a wall of text, so thank you for taking the time to look at it if you do!