the mod: increased % elemental damage with attack skills

i'm assuming characters like mages (that use elemental damages) are the ones that will want this mod on their gears, or does it help all character classes? how important is this mod on items? is it a primary stat to look for in terms of damage?

is %increased damage influence your damage more or does is % elemental damage better?

thanks in advance.

by this link he means it increases the elemental damage you do with an attack skills and not with a spell