Initiation into a Coven provides a test for new candidates, a barrier they must pass and therefore demonstrate their willingness to learn and grow, and which also precipitates a new sense of being within the candidate, and which then helps to bring them into alignment with the Coven as a group of people, and as a collective group mind.
Witchcraft works around a general principle that there are two planes or levels of 'reality'.
All our rituals and ceremonies are specifically designed to cause a resonance on the Inner Planes which then works back into the outer planes to manifestation. The major point of initiation in regard to this is that those who are Initiated are then 'plugged in' to Inner plane powers and resonance's that already exist so that they can work with that from the very beginning and while they are developing their own Inner plane contacts and power connections. If this Initiation occurs within an ongoing tradition it is akin to providing the new Initiate with a well trodden path through the Inner planes to connect with power- a path that is clearly marked and can therefore be more easily followed. Initiation into an established, ongoing Tradition will take you to the door, provide you with the key, and support you when you step through it. From this article you should clearly see the benefits of Initiations of all kinds and at all levels.