Do you need to know your gauge? No. You can certainly crochet without knowing your gauge. But if you want to have just the slightest idea of what size your final work will be, you need it.
Very often the never-did-a-gauge-swatch-chat is followed by a funny story about extremely large or small hats.
It doesn't take long to learn to do a gauge swatch and it might save you hours of frogging for the rest of your life!