I'm making a pure Blizzard sorc and I'm wondering if it'd be worth it to pump points into ES, since I'll be running an Insight merc. Would it be worth it, or would eventually getting a CTA be a bigger bonus to survivability?
What do you think?
EDIT: I should note I'd be maxing Energy rather than Vit if I chose to go the ES route.
My 2c: ES is generally unnecessary in PvM, but if you want to use Insight anyway and can easily get the mana pool (Spirit/Shako/SoJ/Frostburns) to support it without sacrificing too much vit, then really all that mana just sits there unused. I've you're still very poorly geared I'd stay away but if you've got some decent stuff then 1ES/1TK works well, especially with prayer. If you balance your stats right - usually very little into energy - you'll rarely lose too much of either bulb and Prayer/Meditation will quickly fill them up again.
That said, Blizz isn't particularly mana-intensive so *assuming decent gear* you don't really need Insight. Max vit with a Defiance/Holy Freeze merc using someting like Reaper's Toll (or Kelpie Snare for Andy/Meph runs) makes for a tanky build as well.
Mana burn makes full ES builds a little pointless. If you want to max something, then max TK and keep ES at 1
Biggest issue with ES in PVM is mana burn. If you get smacked by a mana burn group that does high damage, you can easily get insta killed once your ES breaks and a few more attacks hit against your low HP pool.
IMO, pump up blizz to full synergies then increase your ice bolt for ice blast/glacial spike synergy instead of going TK/ES. You'll be surprised how fast bosses go down with blizz + a beasty ice bolt.
With Blizz i wouldn't go, if you have an attack thats a low point investment then maybe, my main light sorc is a chargedboltress with full TK/ES, that works quite nice.
If you ARE going TK/ES then you should invest in energy maybe not 100% due to mana burners as ppl allready have stated but quite a bit as return on investment is soo much higher.
Blizzard works with 20 points and 1 in Cold Mastery, in a 1 player game. Not, "blasts away the screen", or "insta-kills Lister". It's surprisingly workable.
Blizzard maxed with 20 points in Ice Bolt and 1 in CM is a killer with a few people in the game.
Blizzard, Ice Bolt and CM maxed can do really effective boss runs.
ES works great with either Blizzard or Frozen Orb, not because of any skill related reason, but because you can build one up and then run Hell Mephisto with absolutely crappy items in Hardcore mode. The efficiency of the builds are incredible. You can also run it in SC, if you like getting a fast start to the ladder items and/or trading. I did it before I played HC.
ES/Blizz benefits: You can tank. Your skills aren't restricted by distance, so you can jump in for your mercenary and maybe he'll survive the run. Blizzard also feels like it scales up against packs a lot better than FO.
ES/FO benefits: Your skill setup is much less restrictive, so you can get everything you want, like maxed Teleport or Energy Shield or whatever.
With the advent of Respec Technology(TM), you can run either build until you get enough wealth to trade them in for a fully synergized attack or perhaps an alternate element for Hell area clearing, or whatever it is people do.