To get max damage out of the lock (especially an affliction lock) you need to work quite hard.

As a single player I would Dot up multiple targets where possible. on trash living less than 15 seconds drop the curses and shadowbolt spam.

You wont get better damage using drain life. Shadow bolts will be the best damage.

On a sustained dps fight an afflock can just go on and on and on. But even this requires decent technique. Applying all dots (and reapplying them when they are dropping off) and shadowbolting continually. Life tap when running out of mana and keep on banging. Curse of doom (amplified curse of doom) every minute.

Unfortunately this doesn't suit a multiboxer group.

I would have thought a warlock would be good for farming the totem of the void - there are some pulls where you would enslave one demon, banish another (if it's the insance I think it is ) but probably requires a bit more involvement than multiboxing provides.