General Build Information
DS/Ruin, also known as 7/21/21 +2, is an underrated jack of all trades build. Demonic Sacrifice's different buffs allows for the warlock to choose between three different playstyles: A heavy damage/nuking mode, an elementalist/AoE'er mode, and a heavy regen mode. DS/Ruin is very solid in endgame raiding and most other aspects of the game.
DS/Ruin puts its points 21 deep into both demonology and destruction for DS and Ruin of course, and in affliction 5/5 Improved Corruption, 2/2 Improved Lifetap, and usually the last two points are put into Suppression.
The "Core" of the build (?/21/21+) http://www.wowhead.com/?talent=AZdxczIbzZxx0tr0z
Sacrificing a felhunter will ultimately give you less mana than sacrificing a voidwalker (3% of max health vs. 2% of max mana), but it has the convenience of giving you mana directly so that you can continue casting nukes. Sacrificing a voidwalker is handy because it makes you less of a burden to healers and can be very nice while grinding, but it if you want mana you need to life tap constantly.
Now with Life Tap gaining from +damage gear even a single Life Tap can put a well geared warlock onto the healing-alert radar of every priest in the raid. Since getting healing from multiple healers every time you Life Tap pretty much defeats the purpose of sacrificing a Voidwalker in the first place sacrificing your Felhunter instead can take a lot of pressure off of your healers.
Sacrificing the succubus pet gives the 15% shadow damage buff. This maximizes the warlock's damage and allows him to play as a nuker/DPSer. Shadowbolt, DoT, Shadowburn, Death Coil damage is all buffed nicely.
Sacrificing the imp gives the 15% fire damage buff. This maximizes the warlock's AoE abilities by giving Rain of Fire and Hellfire more damage. It also buffs the damage of Immolate, Searing Pain, and Soul Fire. Along with Curse of Elements the warlock can choose to buff his fire damage output nicely.
Sacrificing the voidwalker allows the warlock a health regen of 3% health every 4 seconds. Along with Improved Life Tap, the warlock has a very nice rate of health regen and a very nice health to mana Life Tap ratio. This is a nice playstyle for instancing, grinding, and raid bosses. This buff works nicely with the trinket reward from the ST warlock quest. You can summon a voidwalker at no cost (no mana and no shard) every 30 minutes, just as the DS buff wears off.
The DS/Ruin build has the best raid damage available, second only to the 'DS/Rez' technique. Also in endgame, non-sacrificed pets are practically useless and can be a liability(besides the phase-shifted imp).
NOTE: As of 1.12 the 'DS/Rez' bug has been squashed.
7/21/21 +2 locks enjoy all of the PvE goodies in the destruction tree, all of the early utility talents from demonology, 2 instant DoTs, and three solid modes to play in.
DS/Ruin isn't the best PvP build. The succubus and felhunter are useful for their abilities in PvP. If you choose to play with a pet, some will say you have 'wasted' the points in demonology by not utilizing DS. DS/Ruin lacks the burst damage potential of a deep destruction build, and the survivability of a deep demonology build.
Specific Talent Build Examples
This is the basic 7/21/21 +2 build. http://www.wowhead.com/?talent=Ai0bZfxuuM0oZxx0tr0z
Level 70 Variations
Assuming that this build is based around taking exactly 21 points into Demonology (there is very little benefit from going further), and at least 21 points into Destruction, there are a number of different routes you can go beyond that.
- Sac/Heavy Destruction (0/21/40)
With this build you most often sacrifice the imp to give you +25% fire damage. Conflag+Emberstorm are musts, bringing you up to 32 points spent in Destruction. The final 8 points are debatable, this build is only interested in damage output, so these spare points go in Shadow and Flame and Backlash, but Soul Leech, Improved Searing Pain and Nether Protection would also be valid choices, especially for a PvP based build.
- Conflag/Sac (7/21/32)+1
You loose some of the power in the high end of the destruction tree to get instant cast Corruption and Improved Life Tap. This is how ever, a little counter intuitive since one of these Talents is strongly PvP based, and the other is more often used in raiding builds. It may well be that the 2 point in Improved Life Tap are better used to max the PvP centric Improved Searing Pain or Nether Protection
- NF/Ruin/Sac (19/21/21)
This is probably closest to the original concept behind Sac/Ruin. Unlike the 2 builds above, the Succubus is generally sacrificed instead of the Imp. One question this build raises, is that with 19 points in Affliction already, do you not want to continue on till you have Shadow Mastery? ofc, this means not taking Ruin, which takes us out of the realm of this article...