With a filed reed the bark is removed with a definite cut before the vamp is shaped. with unfiled reeds the vamp is shaped straight into the bark. so, what difference does this make? well it's really a reference to the french style of filed reeds and the american style of unfiled reeds.
how the two different styles respond differently has a large amount to do with the mouthpiece style and the player. most manufacturers state the filed reeds have a more focused, flexible tone whereas unfiled reeds will have a more powerful, dark, projecting sound. every player finds their own preference here though so nothing is set in stone but there is method in the madness!!