I believe Jung used it as a nice way to illustrate the mind and its processes (archetypes). Much stays hidden for us, beneath the surface of vinnana. Mind works in a for us hidden way.
In this context one also immediately sees that mind is not the same as vinnana. While vinnana refers to conscious moments, mind can also refer to what is not conscious, not active, hidden, dormantly present and going on. For example, it is said kaya sankhara’s arise in the mind to regulate the breath, but they are not consciously experienced.
Other unconscious aspect are there too such as anusaya which are not yet triggered, not active, but are still present in a dormant way in the mind. Not in vinnana.
There is much hidden in us all the time. There is very much going on beneath the surface of vinnana. We only touch a very small part of reality with vinnana.
The All cannot be defined by vinnana,i feel. It must be defined by wisdom. Conscious moments are a small part of our lives, but in our self-views and self-experience a very big part.
I read neurologist also postulate that a certain neurological treshold must be get over before something becomes conscious. Also decisions are not made that consciously, because, before we experience a decision or choice, it is allready made. It must only get over the neurological treshold to experience it. We might think that we made that decision but that is always the strange point of view of vinnana.
Also things like falling in love, experiencing revulsion or attraction to people, or Dhamma, or whatever one starts to feel and sense with people and in situations, is not at all consciously controlled. It is just a result of what is unconsciously going on and gets over the treshold.
It may look like we are very self-aware, in controll, very reasonable conscious beings, making our own choices in life, but that is, i believe, a vinnana illusion. I believe vinnana is the great magician in the sense that it creates an deceptive world in which we are in controll, in which we make decisions, we are free, in which there is an entity that instigates feeling, emotions, wisdom, love, compassion etc. and is owner of all this.
I think it can be useful to see at the mind or life as a iceberg in which there is very much going on beneath the surface but which we do not identify with, and do not see as our life, and the small part that is above the surface, vinnana, dominates our ideas of what and who we are and life is.