This is a key early, game support unit. It keeps your summoner relevant by threatening to move enemies adjacent to it and by generating boosts. While the Chosen Grove doesn't rely on boosts as heavily as other Earth factions, it still needs some, and this is your only unit based boost generator (all others come from events).
So early on, you want at least one active Seed Bearer to help with control and boost generation. Later in the game, you can start discarding them more freely. I generally try to always keep one ready and boosted.