flash triggers. a question.

[Magic_x_uk]

Hi, just curious what dedicated flash triggers are used for.

As I was under the understanding that flashes can be used off of camera & the camera can trigger flashes.

Ie I have a nikon D80 & if a bought a speedlight 600 / 900 etc I can put it on its stand away from the camera & the camera can remotely make It fire.

So what does a flash trigger dedicated ones do that the camera cannot


Thanks