The reason is that some enemies have a lot of health and many of them can heal. If you disintegrate a target it also can't be raised as a zombie.

If you don't like it (and I'll admit, some of them are a bit underwhelming) mod it later. Unless you're a console peasant, that is

Given that adept level spells were doing 50+ damage they would have to be pretty huge HP sinks to take more than 2 spells after they are below 10% HP, so its use seems fairly limited. I might see it on the higher hit point sponge difficulties though. So yeah to me I think it should have given a chance of it at a much higher HP %. I mean crap its just a chance of it now at below 10%, since it will be saving you a single spell what one in 50 enemies you'd think it would be guaranteed.

If the perk takes effect before damage is delivered, it would be useless.

But if it takes effect after damage is delivered? Then 90% damage would be enough to one hit kill something.

If you only are using destruction for your damage, then this would be a maximum of an 11% damage bonus (sometimes less, depending on how much damage was delivered directly -- but note that other damage boosts can also "waste damage" by virtue of landing on a creature which would have been dead anyways).

And, if you are using other approaches to soften up your targets before unleashing destruction, it can be quite a bit higher than an average 11% damage boost.

Anyways, even if you call it a 5% average damage boost (it's really closer to 11%), it's still something which stacks with your other destruction bonuses.

1. You're comparing lower teir perks to top teir perks.

2. You still need to get some of those perks to get to higher teir perks.

3. 10% still could be plenty of HP left on higher end mobs, and it seems nice for AOE magic damage moves.

Lol 50%? That would be a bit excessive; it could potentially make lightning spells one of the most overpowered things in the game.

This.

I like those perks, it's like your actually able to Favor one of the Elements over the others, i for one am doing that and i'm gonna be using more Frost Spells than others
just wish there was more Perks focused on certain Elements.

Read again!
"a small chance" I wrote (you even quoted it and made it bold).
http://www.gamesas.com/index.php?/topic/1248479-already-some-perks-dont-seem-really-worth-it/page__view__findpost__p__18999401

Good point.
So the question is, how it's actually meant.

I think that some of the first mods out there will be Perks overhaul. So I'm sure everyone will find their best preference.

It seems pretty obvious for me. For example, maybe I don't want to disintegrate enemies? Perhaps I can win battles with less killing if fire makes them flee? There's also the whole thing that they are "perks." Granted the smithing ones are hardly "perks" considering they restrict what you can even make, but in this case they are perks.

What is the HP requirement for the decapitation perk? It gets a 25% damage bonus and a chance to kill, spells have some advantages like AoE, so i see it being lower but not tons lower.

The special attacks get set off whenever you're going to do enough damage to kill and the enemy you're killing is the last one around.

this
and if its anything like nv, might be something to do w better chance of doing critical dmg??

Well all perks can't be the best so at least some you don't exactly need.

I still gotta decide which I want to get.

They are the equivalent of the "chance to decapitate" perk in magic. Maybe they aren't as useful as other perks, but in a tough fight it might save your life here and there, and against several bad guys having one disintegrate or be paralyzed might be helpful. It's not always one on one.

I agree there are probably more prudent perks available, but these are more FUN.

I wish Intense Flames made your flame spells blue to indicate greater heat.

Exactly. I do not understand the fuss over these perks.

Specifically, I think they will be much more useful concerning AoE effects. Multiple targets being hit, or in the case of "chain lightning" ,an already confirmed spell, a spell striking more than one opponent per cast.

Also, I am pretty sure it is not known at what point the effect kicks in.

Option 1: the effect only kicks in when you are attacking a creature already at the 10 percent threshold.
Option 2: the effect kicks in if the spell hits and takes the opponent within the threshold.

If it is option 2 that is wildly more effective, because every creature would essentially only have 90 percent of their health bar in a safe zone. 1 powerful hit could take it straight to the disintegration effect (in the case of shock)

I am betting it is option 2.

As the post above said, assuming only one on one fights, and large damage single shot spells in your mages spellbook is not going to be the case. Many fights concern multiple enemies and/or enemies with small healthbars.