The Void is understood by the Dark Templar and serves two purposes for them. It is from the Void that they draw energy to use psionic powers, as due to severing their nerve-appendages in a display of contempt for the Conclave, they lost the primal link the rest of the protoss share. Although this removed them from the control and discipline the Khala provides, the Void provides the dark templar with psionic powers unheard of by their brethren. The Void grants the Dark Templar enormously strong individual will.
It appears that the Dark Templar associate the Void with death or the afterlife – to "embrace the Void" is to embrace death, so to speak. They consider anything that taints the Void to be unholy, and it is a major part of their religion.
In recent times, certain Dark Templar have mentioned "an ancient voice whispering from the Void," chilling them to the core.
The "currents" of the Void allow faster-than-lightspeed travel for the Dark Templar. These currents are affected by gravity and solar winds.
Void powers enable Dark Templar to resist infestation by the zerg.
Utilizing the Void and Khala simultaneously grants protoss incredible power, but can result in the protoss burning out like a star. Protoss who can utilize both sets of power simultaneously are exceedingly rare. Known practitioners were Adun and Tassadar.
The Void is inhabited by a mysterious entity at KL-2 calling itself the "Heart of the Void". The KL-2 entity "tainted" the Void, according to the Dark Templar.
The xel'naga understood the Void. Their ships possessed the ability to travel through it. The xel'naga imprisoned the KL-2 entity using the powers of the Void.
It appears that the Overmind knew of the Void in some form or another, as the powers the dark templar wield were similar to its own, such powers being the only thing that could permanently destroy its cerebrates and the Overmind itself.
↑Yeah, I mean, basically, any protoss that is a part of the Khala is going to have an enormous psionic energy to draw on and can create, you know, obviously, wepons and blades with it. The dark templar, you know, in all of the lore, they, because they chose to go their own way and they don’t have the power of the Khala behind them, but they have the power of enormously strong individual will. It's sort of, I’m giving a long-winded version of the answer, I think, that Chris just gave. One is pulling that power from within whereas the dark templar have to take what is around them, the void, and manifest it. It is a completely different philosophy, but both are really cool weapons. Chris Metzen, Brian Kindregan, StarCraft Legacy staff. 2010-10-23. BlizzCon 2010 StarCraft II Lore Panel. StarCraft Legacy. Accessed 2010-10-25.