What is the point of skulls in Halo 3?

[Mighty E]

What are the skulls for? What sort of things do they 'unlock'? Are they at all useful in campaign? Once I find one, do I need to hold on to it for the remainder of the mission, or can I just throw it away?

 

[dan]

Skulls are for two things, they are achievements, and they give "extras". Some of them make the game more challenging, and none of them are really useful, they just make things spiced up a bit more. When you find one, as long as you pick it up once, you have the skull saved, and you do not need to finish the level. as long as you've had it in your posession once.

 

[Megan B]

The skulls make the game harder. They are useful if you want achievements (META scoring). You can pick it up and drop it. You can turn them on in certain levels to make the game harder. You have to get them to get all 1000 achievement points and the samurai sword.