Seeing as each class only gets 2 or 3 new abilities in WotLK, each one of these new abilities should have a definite purpose. If it's just going to be spellbook filler then why waste the developer's time making these new abilities at all?
A long time ago Ghostcrawler commented on shadowflame, explaining that's it's useful because "It does shadow and fire damage." The fact that this is completely stupid put aside, what kind of damage it is doesn't change the fact that's its damage, and piss poor damage at that.
What then is the purpose of shadowflame?
The purpose of shadowflame is the snare. Then why does the spell have no purpose unless glyphed? If that's its purpose, it should be the baseline effect.
The purpose of shadowflame is to do AoE damage. Why waste developer's time making a new aoe spell that's completely inferior to seed of corruption and rain of fire's DPS? Warlocks do more aoe damage single target nuking each mob at a time than shadowflame does.
Why does Blizzard nerf warlock survivability because "warlocks are not supposed to be melee tanks" then give them a 5 yard range spell? Are they ranged or are they close ranged? Make up your mind.
Why was shadowflame's only redeeming quality, conflag'ing off shadowflame, nerfed to hell in 3.1?
Why is shadowflame's damage such a joke? I'm not talking bad damage like it needs a 15% increase, I'm talking bad like increase its damage by 100% and maybe I'd think about using it.