Blinkroot

It wants bare dirt or mud with no grass on it, which is why you find it underground and hardly ever on the surface. Light and depth do not matter. If the block underneath ever grows grass the plant snaps off and drops as an item, so a farm sitting next to spreading jungle grass will quietly dismantle itself. It also matures faster below the surface, fast enough that it is the quickest herb in the game to come back after a harvest.

Blinkroot blooms and stops blooming at random rather than on a schedule you can build around. Seeds only drop from a plant that is currently lit, so the mass harvest rigs people use for other herbs do not translate. You end up eyeballing the patch, judging how much of it is glowing, and deciding whether cutting now leaves you enough seed to replant. A Staff of Regrowth or Axe of Regrowth softens that a lot, since a blooming plant cut with one gives extra seed and sometimes a second root.

Blinkroot Seeds go into Clay Pots, planter boxes, or straight onto suitable soil. If you would rather not farm at all, an Herb Bag coughs up both the root and its seeds.

The glow shows through terrain you have not explored yet. A pulsing dot behind an unlit wall means there is open cave back there. It is rough, but it is a free way to pick a direction when a tunnel dead ends.

Mostly potions, with the Biome Sight Potion the one that keeps demand up late in a playthrough. It also goes into the Hanging Blinkroot and the Garland. Journey Mode players can skip researching a full batch of every herb by researching one Garland, duplicating it, and pushing the copies back through Shimmer to split them apart.