Get the recharge up on freezing rain and you shouldn't need it too much. Before you have enough recharge to keep up FR most of the time you might wish you had it. I sometimes wish I have it on my fire/storm, but I still have a 5 second delay between freezing rain applications.
I like to stick aim in this chain:
FR>aim>rain of fire>fireball>firebreath/or st attacks.
Is it needed? nothing is really needed in this game. It makes that aoe alpha chain hit harder, which for me is reason enough to take it. Tohit buffs also accept some very nice io sets.
I picked it up for the damage boost, not the accuracy boost as well.
Arc #40529 : The Furies of the Earth
with all the IOs available now, is the +acc capped or is aim worth picking up?