When using an already stealthy character? I see people raving about it when used in conjunction with an already stealthy character, but I can't for the life of me see the use for it. Yeah, i can see how it would prove very useful for non stealth characters [Mage etc] if you're needing stealth here and there and need to stop being overrun whilst casting powerful spells, so I'm not completely dismissing it.

With sneak already perked, invisibility and muffle are next to redundant. Fear and rally seem to be pretty pointless because 1) I don't want enemies running away only to appear a minute later and 2) I've never had much issues with followers that rally would become a staple. Frenzy, well, i want the one-handed or archery xp, so it would be the last thing I'd want to use.

It can be very funny to play with frenzy spells. But indeed I rarely use illusion, the rally spells are completely useless, they barely make any difference even when you stack rally and courage (not sure about call to arms), it would be much better if they were stronger, lasted longer but didnt stack.

It seems useful on paper, turning enemies on each other, but its a sneak skill. You give yourself away every time you cast unless you have the perk for silent casting; even then you have to see the enemy before they hear you in order to cast stealthily. Its fun to use but the problem is it doesn't seem to fit any play style well.

Controlling the enemy's mind fits a vamp well. Any mage really.

Alonzo loves messing with people's minds. I actually opted for Illusion out of the fact he somewhat resembles a Wraith from Stargate Atlantis, and they originally had powers allowing them to make people see things (and Wraith Queens could bring people to their knees with telepathic powers). Illusion seemed to provide spells in kind, and I've had fun with Fury so far.

It works great for mages agains multiple opponents. Cast frenzy to get them to fight each other then summon atronochs to join the fight then start casting fireballs, ice storms, or chain lightning into the crowd. Be sure to pick the destruction spell that matches your atronoch so the wont be damaged. Alternatively you could cast a destruction cloak then become ethereal and float around the whole group damaging enemies while they are fighting themselves and the atronochs.

Invisibility is extremely powerful.

I think sneak can just be as powerful, especially with shadow warrior perked. I could count on one hand how many times I've used an invisibility potion when playing a stealth character and I've played many. Like i said, I can see it's usefulness with non sneaky characters, so I'm not dismissing the fact it can be a powerful school of magic.

Good for stealth characters I suppose with spells like Invisibility and Muffle, but by the time your sneak is a high enough, you won't need these spells at all. I suppose the other spells are good for a mage's second line of defense when turning enemies against each other or causing them to flee, but summoning Daedra with Conjuration feels more efficient for that role. IMO, Illusion just doesn't seem very useful in Skyrim. Fun to use, but there are better alternatives. I remember using Illusion as a main skill in previous TES games and it helped a lot with getting a good reputation with NPCs.