Novice/Apprentice/Adept/Expert/Master Conjuration-

Blah blah efficiency blah blah basic perk blah blah every mage blah.  If you’re investing a lot in Conjuring things, get these perks.  That is all.

Mystic Binding-

Let’s face it, the weapons you get with Conjure Weapon aren’t exactly very nice.  Any Blacksmith character will probably be able to do better and they don’t have to cast a spell, they just pull the thing out.  Surely you can spare the 8-25 weight units for the weapon you intend to use all the damn time, right?  Yeah.  Mystic Binding, at least, keeps the weapons much more competitive for a lot of the game.  They still aren’t worthy of looking at when Daedric weapons are available, but the 50% increase in their damage goes a long way towards making weapon conjuration viable, rather than a crutch for when you just don’t want to bother smithing anything.

Conjuration Dual Casting-

This one is a little weird to consider.  Conjured animals and weapons are so quick to conjure that there’s really no reason to invest in two-handed conjuring for a mere increase of duration.  If, on the other hand, you’ve decided to be a necromancer and raise dead bodies to fight with you, you desperately want this perk.  It’s impossible to raise a pile of ash, after all, and sometimes you just don’t have a corpse available.  That makes the dual casting effect hugely more useful.

Summoner-

Probably the best use for this perk is to ambush your enemies with an Atronach right behind them while you’re at a great distance, or even in hiding.  Raising undead from a distance is much less useful, since most of the dead bodies you run across are ones you made and you cleared out your enemies in the process of making them.  Dungeons with smaller rooms also limit the utility of the summoning range rather harshly.  Outdoors, though, where you find giants, mammoths, dragons, and some other bigger nasties, this perk can give you a lot of direly-needed breathing room when you go on the attack.

Soul Stealer-

For all Conjuuration-Enchanters, this perk has the immensely useful effect of making all of your conjured weapons gain the Soul Trap enchantment.  Even Blacksmith-Enchanter-Conjurers will find this a useful effect, since it allows you to -not- have a second weapon with Soul Trap enchanted on it that you switch to when killing something.  That can save you a lot of weight, crafting, time, and a lot of those same soul gems you’re generating by possession of this perk.  Useful!

Atromancy-

This is... mostly useless.  If your Atronachs are lasting long enough to make you recast them, you’re unlikely to be out of Magicka when they die.  And since Atronachs summon at instant speed with no investment other than Magicka, there’s no reason not to just resummon them.  So, for the most part, this is a waste of a perk.