The seed coat stays intact until the proper conditions (temperature, moisture, lightness, or darkness) present themselves for the plant to emerge.
Once the temperature feels just right, and there’s enough moisture to cause the seed coat to swell and rupture (thereby releasing its food stores and coaxing the embryo to develop), you have germination.
If the seeds are already wet, and the seed coats have absorbed enough water for the first root to emerge, that could mean a much earlier harvest than sowing seeds that were dry.
Soaking is beneficial for pea seeds as well as other seeds with thick, hard coats. You can (and should) soak the seeds of fava beans (Vicia faba), beets, cucumbers, corn, and squash. Big seeds. Wrinkled seeds.
In general, the tougher the seed, the more it will benefit from soaking. You can actually soak any seed in water, including flowers and herbs, though I feel the smaller ones are too troublesome to work with when they’re wet.