Caveat, I'm a newb and this is my opinion.
I did the math a long time ago. Depending on group makeup and kill speed you can really just fall into 3 categories.
1. Fastest kill speed, <12s, mana drain for casters in group and maybe nuke with DD.
2. Medium kill speed, ~12s-24s, Mana drain, maybe debuff scent if necessary, 1 dot if > 90% hps, rest Nuke with DD.
3. Slow kill speed, ~24s+ per mob, Mana drain, debuff, 2-3 Dots if hps > 80%.
This is assuming you are doing the mez and park mobs. If you're killing a lot and not mez'ing, then start dotting things the tank isn't targeting and see if you can get agro. This skyrockets dps a lot if you spread the dot love around. Or tell your tank to start targeting different mobs and you can dot those > 80% hps and once 2 or 3 dots on a mob, switch targets.
Necros are really not meant for the 90+ era group game as a DPS class unless doing the target switching, mobs just don't last long enough. They are the ace in the hole for nameds when they explode, and then debuff/mana support when killing normal mobs.
