Seed Tiberium is a Nod support power used in the Third Tiberium War. An Armageddon Bomber flies over the battlefield and sprays the area with Liquid Tiberium, accelerating The growth of Tiberium in that area. Seed Tiberium is activated at the Tiberium Chemical Plant.
The moment the bomb is dropped, Tiberium crystals sprout out from the target area. Anything directly under the bomb will take some damage, and infantry will be noticeably affected in particular if they are vulnerable to Tiberium radiation. However, the damage from using this power offensively is negligible and using it in such a way may end up giving your enemy more tiberium to harvest. The primary purpose of this power is to keep Nod's economy running well into the late game; the power costs 500 credits to activate, and when the 'seed' hits the ground from the Apocalypse bomber, it instantly spawns more than 500 credits' worth of Tiberium crystals, allowing a Nod player to make extra money upon harvest, especially if the crystals are given enough time to spread out and create more Tiberium before harvesting. Ideally the player could use this near a refinery in your base, since that is probably a relatively safe area and allows for a quick and efficient harvest.
There are few opportunities where it is a valid excuse to use this power less than as often as possible since it is almost guaranteed to give the player more than he spends on it, unless the spawned crystals aren't harvested by him/an ally or are somehow destroyed. There is also the rare instance where having more spending money right at the very moment is more important than investing in the long-term, in these circumstances it is also valid not to use Seed Tiberium.