i think of it like this:
i want my forearms to fail in order to get max gains from them,
but if they are only being worked during compound lifts like deads, rows, etc., then i dont want them to fail, b/c this means they are holding my other muscle groups back during those lifts.
so the...
for me, they are important. i have seen good results in the past year or so since i started working them directly. Also, i immediately saw weight gains in my back/bicep lifts afterwards. i work them off and on now, when i have extra time after arms.
I figure, weak forearms could really hold you...