Is it important to knead biga/poolish?
Well, technically there is a minor difference between biga and poolish, but often the terms are used interchangeably. 

Just for clarification:


A poolish uses equal parts (by weight) of flour and water and very little yeast (sources vary between 0.1% to 1% fresh yeast / 0.03%1 to 0.33% dry yeast of flour weight). This leads to a poolish being rather liquid and easily mixable with a spoon.
A biga has a lower water content, usually in the range of 40% to 60% of flour weight and a yeast content of 1% fresh / 0.33% dry. It will be quite firm in the beginning and may require some kneading to mix dry and wet ingredients properly.


But should you explicitly knead?

Actually, you don't need to. Both pre-ferments will rest for hours. During that time the gluten will both develop (-> see the principles of no-knead bread) and be diminished to some extent by the growing yeast. You don't want or need to mess with this process. Just mix flour, water and yeast until somewhat homogenous (no dry patches) and let both yeast and enzyme activity do their thing. You will observe that the "uneven" preferment will change texture over time, yeast starts to bubble and when it's ready to use, it will be nice and even.



1 Yes, that's a really, really tiny amount.