How does the quiet casting perk work? Does it make a sneak Mage fun or viable?

It's pretty cool when you are near enemies and need to cast a spell, or want to cast a spell which would give you a bounty.

Totally worth it for any mage who also sneaks. It keeps you totally undetected while casting. Great for buffs and any other spell that doesn't not directly affect enemies. They will still run towards you if you use damaging spells but they won't know exactly where you are. It's almost a requirement for an illusion/conjuration sneak mage. I use it on mine and am never seen unless I want to be.

Same as muffle, only affects sound, not light. If you are in line of sight, you may be detected casting a spell, but if you have a spell ready to cast and not loosed, as far as enemy AI is concerned it sheds no light, however bright it may look in your hands.

Use it on my illusion based assassin mage. If you're like me and use fury/frenzy a lot (great for assassination targets) then it'll allow you to remain hidden while the enraged target locks onto the nearest target. Without it I've had frenzied mobs ignore anything closer and head straight for me.

As the Perk states, ALL of your spells are silent to other when cast. Meaning if you can sneak up behind an enemy, you can cast even Master spells such as 'Firestorm' completely silently (which happens to be the exact way I completed a Dark Brotherhood contract and cleared the room at the same time... ).

I like nothing more than to Sneak into a room and see a group of four or five Bandits/Falmer, and dropping two Dremora Lords right into the middle of their gathering. Then (while still hidden) start pelting the whole group with 'Thunderbolt'.

It makes being a Mage soooooo much more lethal (to your enemies).

So yes, the Quiet Casting Perk is very, very nice for any type of Sneaky Mage.

It come's in handy as, Destruction spells always blow your cover before they even hit the target.

I think it's a must for any character type that uses magic. Everyone wants the element of surprise-to be able to get that clean first strike and then at least one more before the enemy can touch you. Casting the mage armor spells seems especially noisy so if you use Alteration a lot, then get your Illusion up to 50 ASAP and grab the perk.

Essential.

If you use sneak at all on your Mage or even Assassin that simply uses Illusion, I'd say it's a must. Before getting it, you'd cast a lightning bolt and become detected immediately. After acquiring it however, your destruction spells work pretty much like a bow would work in sneak mode. Shoot stuff at them, and they'll start looking for you, but if your sneaks good you can pretty much kill everything before they even know what hit them.

Also, just like using a bow, you can shoot a spell somewhere random on the ground and the enemies will all go to that spot to see what the noise was, similar to an arrow hitting the ground/wall or using Throw Voice shout. It's quite useful to cause a distraction.

It's certainly worth it if you play a sneaky character who uses magic often.

Casting lightening storm while sneaking and not being detected? That's epic trolling right there.

Casting a cloak spell and becoming invisible or using Ebony Mail and becoming invisible is always fun too, although that can be done without Quiet Casting lol

I agree with the things said above (except what Virtuosus said about invisibility). I have quiet casting and it is awesome as they stated. To be able to keep your "xFlesh" protection spell up without the danger of alerting opponents = nearly priceless. I am now attempting leveling up using a sword in each hand, as most of my other attributes are maxxed out, and I can sneak up behind an enemy, cast Ebonyflesh right next to them just before 3x damage from my Daedric "legendary" swords from surprise attack; and am now still protected for a minute via Ebonyflesh from any subsequent attacks from nearby opponents. Deadly am I, even without enchanted weapons (you level up faster without the enchantment).

As far as Invisibility goes, it is not that great. Do anything other than sneak, and you become visible. Drink a potion such as fortify X or regenerate X, and you are visible again. Go through a door to another cell/zone and you are visible. Invisibility is quelled in Skyrim.

sneaking mages need it, otherways not.