Zerg's power units vs massing units

It's all about larva: drones(workers), power units (a unit getting some of to by more time or build more drones) cheap on larva, massing units (high numbers of dumping a lot of your economy into.

Expense on larva, if you need a lot to spend a lot of money (zerglings expensive on larva, ultralisks are cheap on larva) - I'm going to defense this attack with 20 zerglings or 5 roaches (being larva-efficient)

The difficulty of when to begin massing units as zerg and when to return back to drone production.

[replay]
ROOTslush(Z) vs Phoneix(T)

• 15 hatch, 14 pool (skipping extra drone), overlord on 17
• Aggressively sending drones by to mining when dealing with a bunker rush
• Doing the "0 larva" stuff (Queens and spine crawlers) and getting upgrades early
• Over-production of zerglings with multilinks, while continuing to make drones

[Q&A]

• If you are going hydralisk and roach does this massing still apply?
• What is your opinion of the Muta/Ling aggressive style vs. a turtly toss?
• If nothing happens when he builds all those units for aggression, does he fall behind in any way?
• How can Zerg measure effective macro?  Other races can use constant production, but how should we?