I know you get achievements for finding them but some of them make the game harder. why do you want them then?? I'm just wondering

i just want them to get the armor and use the grunt birthday skull
also those ''gold skull'' duble ur points so u can get the points acheivements faster
and if u get every single achievement u get all the armors PLUS the katana sword(just for show)
other than that i wouldnt use them

OR, some people would use them to challenge their skill on the campaign.

so when you find it you dont have to use it right?

Exactly. They just make the game more challenging and lots of people like that (me in particular). Also, they help a lot with getting the metascore achievements.

Thanks for the info guess im of finding the skulls i got 2 now.

People want skulls for:
-Achivments.
-the Armour
-Using SKulls get you better score.=Achivments

some of them unlock special abilities like changing graphics and becoming invincible

xbox 360 gametag is motxbox