Dots run a long time. Trash dies in a short time. Using dots on trash means they die before the dot has time to go bang. To get more bang for your buck be smart about killing trash and do it different from bosses and grinding.
Which dots? The answer surprised me.
Here’s a graphic of a few casting sequences:
1: Shadow Bolt Spam
2: Corruption+Shadow Bolt
3: Unstable Affliction+Corruption+Shadow Bolt
4: Immolate+Shadow Bolt
At my current progression, my best casting sequence for Trash pulls (where the trash is going to die quickly) is Shadow Bolt spam. I’m concerned that starting off with a Shadow Bolt may pull aggro.. so I’m planning to actually start with Curse of Shadows (CoE after 2.4.3) and then do Shadow Bolts. I think that will give the tank enough time to build sufficient threat.
[Edited to add: I've actually be doing Instant Corruption and then sometimes CoE followed by Shadow Bolts. The Corruption gives the possibility of instant Shadow Bolts. ]
Unless the mob lives for longer than 27 seconds, even as affliction, Shadow Bolt spam is my best option.
That said.. on something like Curators sparks, Immolate+SB may be superior just because it gets lots of damage onto the spark quickly.
UA, Affliction Spec’d Warlock with insta-cast corruption and ~1300 +shadow damage. Actual averages taken from a WWS of a run through Zul’Aman.
Average Shadow Bolt: 2042
Average Unstable Affliction Tick: 539
Average Corruption Tick: 560
Average Immolate Direct Damage: 510
Average Immolate Tick: 243
My working Spreadsheet