When they were first introduced in the Burning Crusade, the Infinite Dragonflight was deeply mysterious. They did not appear in the Battle of Mount Hyjal raid, even though quest dialogue implied they were doing something there (in fact, that raid was mostly just a recreation of the final mission from Warcraft III in WoW-form.) But the Infinites showed up in both Old Hillsbrad Foothills as well as the Black Morass dungeon, and in the next expansion, they would appear in the Culling of Stratholme dungeon (actually also a Warcraft III mission recreated in WoW.)
The Infinites showed up only at the very end of Old Hillsbrad, without a ton of explanation for their actions other than "Kill Thrall!" But they are the only enemies in Black Morass (other than the non-elite optional creatures in the swamp) and they have a set of trash pulls and a boss in Old Stratholme.
What's interesting about these appearances is that in both, they claim to be trying to prevent bad things from happening. And certainly, in both of these dungeons, bad things happen. The Horde may have redeemed itself, and even proven instrumental in the defeat of the Legion in the Third War, but history might have gone in a very different, more peaceful way for Azeroth if Medivh had been unable to open the Dark Portal. Likewise, Arthas' massacre of Stratholme was the turning point that drove him to Frostmourne and becoming the heart of the very thing that he hated most of all.
Both of these are pivotal moments full of "what ifs," but the Bronze Dragonflight had been charged with maintaining the one true timeline. Unlike our adventures in Draenor, which took place in a parallel universe and thus did not have any paradox-inducing effects on our own histories, the implication is that we are truly ensuring that familiar history takes place by running these dungeons.
The Infinite Dragonflight moves to change the past to affect the future, but what is their true aim? They argue with us as they fight us in those dungeons, claiming, quite correctly, that by ensuring the familiar flow of history, we are ensuring horrific pain and suffering on the world.
While there are some brief appearances of the Infinite Dragonflight outside of dungeons, the only other major interaction we have with them directly is in End Time. End Time is set in a post-apocalyptic future in which we failed to prevent Deathwing from bringing about the Hour of Twilight. It is here that we face off against Murozond. We are there to stop him from preventing us from traveling to the past in order to retrieve the Dragon Soul before it was corrupted into the Demon Soul, and of course the Dragon Soul, wielded by Thrall, allows us to kill Deathwing once and for all.
Murozond, much like the rest of his flight, claims that he has been working toward a better future. It's a much harder sell, though, because he claims that the blasted ruin of Azeroth populated only by ghosts is better than what the "True End Time" would look like.
It is in End Time that we get the confirmation (hinted far earlier in quests within Dragonblight during Wrath) that the leader of the Infinites is actually Nozdormu. Nozdormu appears to be fated to eventually become Murozond. The Infinites are, it would seem, actually the very same Bronze Dragonflight we've been helping all this time, but corrupted and transformed.
But what if they're not?
Nozdormu, when he was made the Aspect of Time, was given a vision by Aman'thul. It was in this vision that he saw Murozond die within the End Time at the hands of his mortal allies. When you defeat Murozond, Nozdormu indicates that he knows this is his fate, and seeing it in person in addition to the vision all those years ago has made his fate perfectly clear.
We can perhaps extrapolate from what we know that at some point, Nozdormu will decide that he does not want to die that way, and in his efforts to re-engineer his fate, he will become the very thing that he has spent his life fighting.
But there's an issue there. The End Time, as we saw it in 4.3, will never come to pass. Deathwing was killed and blown into a billion tiny embers, and the Hour of Twilight was averted. Now, it's possible that lore-wise, that future has simply been erased, and that we only remember it because we're the time travelers.
But with Warlords of Draenor, we've discovered that there are many, perhaps infinite other realities. Many people we know and are familiar with have doppelgängers out there in the multiverse.
Because our actions in End Time were what prevented End Time from ever happening, it would seem that, to avoid a paradox, it would have to exist within a parallel universe.
And if that's the case, perhaps Murozond was never truly our Nozdormu. Perhaps the Infinites are not our former Bronze friends, but are truly invaders from another reality.
In the novella Dawn of the Aspects, it seems implied that the Dragon Aspects didn't interact personally with the Titans when they were given their powers. So it's possible that Nozdormu's vision was just as cryptic and unclear as the kind a mortal might receive.
Nozdormu saw a version of himself, twisted and corrupted into an Infinite Dragon, and assumed that if there was "one true timeline," that would have to be his future self. He might then consider this a way to keep him humble, given the vast power he had been given.
But what if this vision was not a "remember thou art mortal" memento mori from the Titans, but actually a warning to say "this guy is going to be a big problem that you need to deal with." And now, with the Hour of Twilight averted, Nozdormu can relax, or at least focus on other imminent problems (like the invasion of the Burning Legion.)
Kairoz had given everyone a scare, going off and possibly starting the ball rolling on the whole Infinite Dragonflight movement. But Kairoz died, and ultimately the Iron Horde folded like a paper tiger, certainly with no Infinite Dragon holding its reins.
So it went for Murozond, but perhaps Nozdormu is finally free of his terrible burden, with no need to prepare his own people to resist him when he turns to corruption.
And it might be those very thoughts of relief that start him on the path to darkness.