Scarification basically means scratching, breaking or weakening the coating of the seed to soften it, therefore making it easier to reach the moisture and gasses it requires to germinate efficiently.
Because of its naturally aerated structure, coco coir is almost impossible to over water. In fact, coco coir can hold up to 8x its weight in water, and rather than over-saturate, will simply reject what it can't absorb comfortably. If you provide too much moisture to peat bases, for example, you run the risk of water logging. Not so with coco coir.