I realize this is pointless to explain, but just for fun:
Let's assume we're tanking a boss, and we don't want it to be moved to a specific position away from where it starts. We want it to remain relatively close to where it begins and faced away from the party so that melee can hit their positionals and everyone doesn't get cleaved if the boss has one.
So first off, we want the boss "active" as soon as possible to allow our DPS to start hitting the boss as soon as they can. To accomplish this we want to get our own GCD ticking as soon as possible, meaning that we basically want to pull from a range and then make sure the boss is where he should be.
To do this, we have 2 options:
1.) Unmend
2.) Plunge
Both are ranged attacks and both set the boss to "active" once damage registers. Now that we know our two options for pulling, let's explore which will work better.
First it's important to note a similarity between the 2 - both are 15y in range, meaning that you need to be the same distance from the boss regardless of which you use first. Now for the differences: Unmend is on the GCD, whereas Plunge isn't - what this means is that by using Plunge first instead of Unmend your GCD won't actually be ticking and you'll be animation locked until Plunge finishes. Unmend uses a small bit of MP, Plunge uses nothing. Unmend requires you move toward the boss (unless you intend on moving him somewhere else), Plunge puts you directly on the boss. Unmend is 150 potency, Plunge is 200.
Now, looking at that you might think opening with Plunge is perfectly viable - it's 50 extra potency and getting the CD ticking ASAP will get it back up again ASAP. However, Plunge is off the GCD - this is extremely important. Let's look at 2 example pulls based on Drkdays' post about their opener:
Plunge (200) -> Unleash (100) -> Hard Slash (150) -> Spinning Slash (220) -> Power Slash (300) = 970
Unmend (150) -> Plunge (200) -> Hard Slash (150) -> Spinning Slash (220) -> Power Slash (300) = 1020
So by opening with Plunge we get less potency and less enmity due to Unleash. If we remove Unleash we have even less burst enmity in our first GCD. This isn't even considering the optimal use for Plunge, which is after BL, TA, and SE are up.
So now that we've established that it's worse potency/enmity-wise, let's look at the other argument - it gets you on the boss quicker and therefore let's you turn it quicker.
Unless the boss immediately does Gobhook then this doesn't matter. I am not bothering to type up a giant paragraph on this because literally there is no use in turning the boss quicker on the pull unless doing so stops it from cleaving the entire party immediately. If a melee is going to miss a positional with you pulling with Unmend they'll lose it with you pulling with Plunge, it's not enough of a difference to change anything at all.
So, in conclusion, there is no merit to pulling with Plunge. It's use is to close the gap between you and the thing you want to hit, but you also have a thing that pulls the boss that's on the GCD. After you use the pull the boss thing, you can then use the thing that closes the gap between you and the boss if you refuse to just walk to the boss. If pulling with Plunge has been working for you, cool, continue to do it if you'd like, but don't try and argue that it's actually a thing people should do.