Strong and unpredictable early game, solid middle game, strongest late game. It also has some of the best units in the game: zerglings, mutalisks, defilers. Especially defilers, they are arguably the strongest spellcasters in the game

Production speed scaling due to hatches.

If you want 6 carriers at the same time, build 6 starports.

If you want 6 ultralisks or 6 mutas at the same time, build 2 hatches (which you already have)

One consequence of this is that changing army composition as Z is very easy.

Defilers