Most recipes that I see for soy and nut milks ask you to soak the seeds and discard the soaking water.
The only plant milk recipe I've used that keeps the soaking water (Scratch Soy Milk by Andrea Nguyen) turns out just fine.
I've also experimented with using the soaking water in almond milk, and this too is fine.
So why should I discard the soaking water? Is it just a matter of taste, or is there more to it?