There are huge amounts of strategy considerations playing a necro
For example:
How to handle heroic groups of 3?
Strat #1: Send in the pet. Try to burn down pet's 1st target, then 2nd target, then 3rd target
Result#1: Failure. Pet can't stand up to the punishment of 3 single-ups for the time needed
Strat #2: Start with root. Send pet in on one of the 2 incoming mobs. Try to get pet with aggro before mobs kill you. Then go back to burning down. reroot as needed
Result #2: too dangerous. If pet doesn't immediately take aggro (maybe 50/50 at best), necro is crushed by aggro from two single-ups. Nice idea but not enough mob dps removed from fight.
Strat #3: Root mob A. Sic pet on mob B on incoming. target C and fear / root mob C. Burn down mob B while rooting to keep A/C under control. After B is dead, shift pet to mob A and lead with a stun (helps pet build enough aggro to overcome your initial root). After B is dead mop up mob C 
Result #3: Pretty good results. Generally win. Sometimes aggro transfer can be tricky.
Strat fails with group of 4 generally...what to do? Maybe pull with snare from max range? pet on one? root one? fear one?
You get the idea...dream up your own better strat
Post 50, drawing of souls and charm undead are making my head spin with strategy possibilities. Using 3 spells from drawing (hp buff on pet, extra swarm pet, pet heal) on the pet + adding dps of charmed undead + adept3 or better spells makes handling blue ^^^ possible if very risky. sequence of casting makes a huge difference though. Do you cast swarm pets early? Do you cast mitigation spells early (like stun) so they can cycle for a 2nd use? Don't forget to spot heal prior to casting your siphon life and not the other way around! What pet buffs should you use with this combo? I don't know!
Sorry for the rambling, but you get the idea. I'm up to my eyeballs in strategy considerations lol!
However, I agree, not much strat needed to take out blue solo mobs though.
GS