Sure, I'll bite.
Necromancy is a really, really useful skill. It's my favorite skill in the game. I've played two Necro/Mages pretty extensively in PvE and PvP (one on Chessy, one on Siege), and I've played variants of Necro/Dexers (Vampire/Samurai and straight up Necro/Dexer).
It depends on what you're planning to use Necromancy for. If you are PvPing, you need Necromancy at 105 after items. This allows you to cast Wither 100% (incredibly useful area effect spell which has a low mana cost) and Strangle at 100% (everyone hates strangle! it's a damage-over-time spell which does damage based on your target's current stamina. it also interrupts and, the higher your spirit speak, the longer it lasts). Beyond 105, the next breakpoint is 120 Necromancy to cast 100% Revenant. This is great to cast on stealthers since it will follow and reveal the stealther even if they smoke bomb or restealth, all while constantly doing damage.
Depending on what you use Necromancy for in PvE though, you may not need 105 Necromancy. The really useful stuff in PvE for a Necro are the forms. You can change into Wraith Form (leeches mana based on your melee or spell damage), Lich Form (grants insane mana regen), or even Vampire Form (gives you considerable mana and stamina regen, life leech capabilities, and automatically cures all but lethal poison). You may only need enough Necromancy to cast these forms if you use them. You can even use jewelry to get +Necromancy skill, cast the spell, then put your normal jewelry back on (I think, it's been a few months since I played).
Other useful spells --
Blood Oath (PvP) -- whatever damage is done to you is reflected back onto your attacker. It has the side effect of making it suicide to stack combos onto you when you have a person Blood Oath'd. It's really good to let someone cast Explosion on you, then quickly Blood Oath them, then start your own offense. Their explo damage will stack with whatever damage you do to them. If I get this casted on me, I spam interrupts, locking both of us down. It kind of sucks when you get blood oath'd by a necro/dexer.
Corpse Skin (PvP or PvE) -- increases fire or poison damage by a lot (-15 Resist). Great to cast on champs, peerlesses, so that your team's fire damage will get a boost. On Siege, where people have lower resists, I can redline someone with an Explo/FS if this is up. Two mages focusing on a corpse skinned target will drop it, very fast.
Evil Omen (PvP) -- not sure if they fixed this. You can Evil Omen -> Poison or EO -> Paralyze, or even EO -> Mana Vampire. They won't be able to resist the spell, regardless of their resist skill.
Summon Familiar (all) -- Wisp is good mana regen boost, wolves for stamina regen, horde minions are awesome at a champ spawn since they pick up stuff on the ground.. in this case, all those piles of gold. Which I think is fair since necros do all the withering/working of spawns.
Curse Weapon (all) -- For a meleer, this will give you a BIG chunk of life leech. Not sure if they nerfed it since I haven't used it on a dexer in a while, but I would be pretty much invincible, even against things like doom bosses, with this up and in vampire form.
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All these skills mean that Necromancy is an amazing skill in PvP or PvE for certain templates. In PvP, you want to push Spirit Speak as high as possible as a necro/mage to increase your damage and curse effectiveness. It's a little less restricted in PvE, and you can get away with lower. There are a few other spells in Necromancy besides what I mentioned, and a lot of them have very creative applications. I definitely recommend it!