I'm watching Day Daily #194 and he just said something like that:
Rely on 'power units' - they are low on larva. So that way you can spend the rest of your larva on drones.
What does it mean? Which particular units?
found this on TL
Larva is specific to Zerg.
The power units in Zerg are Infestors, Mutalisks, Ultralisks and Broodlords.
Why is this particularly important for Zerg? Because unlike Protoss and Terran, which have dedicated production buildings, each unit made for a Zerg army means one less drone.
Take the scenario where a Zerg needs to kill 5 marines. Instead of making 12 zerglings, which costs 6 larvae (6 less drones), the Zerg can make 1 ultralisk and 5 drones (assuming resources aren't the limiting factor).
This actually relates to another interesting discussion in Theorycraft. When engaging a Zerg army, it's generally good strategy to target down the "power units", the ones that have high gas costs (infestors, mutas, ultras, broodlords), because gas is a limiting resource.
But some people argue that it can be useful to target units that have high larvae cost, mainly zerglings. Since zerglings need to used in large numbers to be effective, replacing an army of 60 zerglings indirectly hurts the Zerg player's potential to pump drones and scale the economy.
Units that are costly in resources, like Ultralisks or Brood Lords.
Units like zerglings or roaches are high on larva.
If a unit is "larva-cheap" it costs proportionately more per larva; this allows you to remax quickly without using too much larva.