You know the drill by now. If you want to use these spells with any regularity, you should get at least one of these perks.
This is useful early on- not as great later. Animals only get so strong, really, but this helps you tons in the earlier half of the game.
Illusion Dual Casting-
As with all other Dual Casting perks, you have to have the same spell ready in both hands to use this. Unlike other Dual Casting perks, though, chances are fairly high that you’re going to be completely okay with this- most Illusion-focused characters like to sneak around and toss their spells from hiding without ever coming out into the open, so it’s unlikely they’re going to need a different spell on hand (hah!) for any situation. This is also one of the stronger Dual Casting perks, increasing spell duration to more than double and directly doubling the highest level targets affected by the spell. If you intend to use Illusion spells at all after level 40 or so, you’re going to need this quite badly- so go ahead and get it early on and reap the rewards from the beginning.
While this only affects Calm spells and has the smallest boost of the level-affect boosting perks, it’s not bad at all. Between this and Animage, your Calm spells will affect animals 16 levels higher than they would have- 32 levels higher when you’re casting with both hands. This is even stronger with Kindred Mage on people, netting you 20 or 40 additional levels onto the effect cap, combining with Dual Casting to make all of your Expert and Master level Illusion spells affect pretty much any humanoid you care to find.