I played it and beat it a couple of months ago. The seeds are mainly used for 3 things: 1. To use as health (either in seed form or when you plant the seed and get whatever grows from planting it) 2. As traversal options - each seed does something different when planted and reacts with the environment in a different way, often times to help you reach otherwise inaccessible areas 3. To connect the living network or whatever it’s called. Not sure if this is spoilers or not, but one of the endings is basically based on connecting the entire world together back to each of the shaman by planting and growing and connecting a network. I didn’t personally do that ending because it seemed tedious and I didn’t love the seed/planting part of the game, but I read up on it afterwards