ahaha, another noob here giving his opinion...
from what ive heard, the adj cam pulley do give you some extra HP if its tuned properly, most frequently it would be used for cars with high cams as they could fine tune their cams to their liking, as we all know, high cams sometimes are a pain in the you know where when it comes to idling and all, so adj pulley might help a lil...
my opinion only larr...havent tried it yet due to shortage of funds :P ekkekeke :P but i believe it helps lorr, like what fritz had mentioned earlier, low end power or high end power :D