This build offers 1 extra drone compared to a typical 9 Pool 9 Speed opening, making it more sustainable over time. However, the downside is slower Zergling speed, so play defensively and avoid pushing out against faster builds like 9 Pool 9 Gas.
Zergling builds are low economy and rely heavily on winning fights. Every time you win a fight at the center, add 1 or 2 drones depending on how many units you killed.
If you’re consistently losing, you’ll have no choice but to keep making Zerglings. It’s better to avoid engaging unless you're confident in winning the fight.