What is Armlet toggling?

I've watched a few live games where Lifestealer's health appears to drop fairly significantly after a fight, without him taking damage. People in chat have called this "Armlet toggling", and while I understand that the Armlet increases stats at cost of HP per minute, I don't understand how the toggling works, and how it results in a chunk of health disappearing at the end of a fight.

Can anyone explain the method, and the purpose of this method?

Thanks!!

The Armlet of Mordiggian currently "Gives +31 damage and +25 strength while active, but drains 40 HP per second." This life drain means that you usually can't keep it on all of the time, but the damage makes it beneficial to turn on when you're fighting enemies.

However, it also gives you a lot of strength, which increases your HP by 19 per point. This means that turning on the armlet gives you 475 HP, although 6.79 made it gradually increase over 0.7 seconds. Turning it off drains this 475 HP away, but it can't kill you. So if you have the armlet activated and you're under 475 HP, you can quickly turn it off and back on again, which will drop your HP down to 1 HP for a split-second and then increase it back to 475 HP over 0.7 seconds. This can be a beneficial way to heal yourself for a little bit more fighting or to tank a projectile or something, as long as you take care not to get hit in the 0.7 seconds it takes to replenish your health when you turn the armlet back on.

Armlet toggling consist in activating/desactivating (toggle) the item Armlet of Mordiggian. This serve a specific purpose :

When activate, the Armlet of Mordiggian will give you 475Hp over 0.7 second. This allow you to have a quick burst of HP that you can do infinitely : Turn it on > gain 475HP > Turn it off > Back to 1Hp > Turn it on > Back to 475HP etc. If managed properly you can toggle between each attack of your opponent thus becomming very hard to kill since you put your health back at 475 every 0.7sec.

You can have more detail on the Wiki

From the Dota 2 wiki:

By turning on the armlet you will gradually gain 475 hp due to the strength it gives you. You lose the health again when you deactivate it, but you cannot go below 1 hp. This can be used to your advantage. If you are below 475 hp, you will lose all but 1 health. When you activate it again (quickly, so the enemy won't have time to kill you when you're at 1 hp) you will end up with 475 hp, more than what you had before. This can make you survive much longer.

The toggling trick is used to give a burst HP increase, increasing your survival time in rough situations if timed right. When you're about to die, you can back off then toggle Armlet for the extra 475 HP, but you should mind the following:

Unholy Strength STR gain is provided over 0.7 seconds.

Unholy Strength has no toggle on or off cooldown.

So if you instantly toggle Armlet, the full HP increase will be provided over 0.7 seconds, as it is stated above. That means it is not advised to ninja-toggle when you're taking hits from the enemy.