There are three types of consciousness we experience: Deep Sleep, Waking and Dreaming.
The relative rate of Time runs differently in each state. While inside each state, time is experienced as if running at the same rate - because our thinking can only be at the speed of thinking. But a huge amount of subjective experience can be fitted into a dream of a few minutes; while hours of Deep Sleep may pass without any awareness of time having passed...
To use an audio analogy; from the perspective of our Waking consciousness, playing a vinyl LP recording at 33 revolutions per minute (rpm); Deep Sleep sounds something like it was recorded at 33 revs per second - so at 33 rpm everything is so slowed-down, that it sounds like almost nothing happening except low groaning noises... Whereas a Dream sounds as if it was recorded at 33 revs per day - so that when played at 33 rpm the audio is so fast as to be incomprehensible gabble.
Or, with a video metaphor - from the Awake state, Deep Sleep is so slow that it is like a still picture, a photograph; while Dreaming is on ultra-fast-forward.
A Being living in Deep Sleep would see our Waking life whizzing past in a blur. (This looks to be what is happening when a waking person tries to interact with a sleep walker - who is in Deep Sleep; the sleep walker stares uncomprehendingly in response to blurringly fast movements and sounds). Whereas a Being in Dreaming time would see our Waking lives in slow motion; every moment 'dissected' into a sequence of tiny sub-components; like the super-slo-mo action-replay, analysing the precise details of releasing a cricket ball from a spin-bowler's fingers...
It is this difference in the relative speed of experience in Deep Sleep, Waking and Dreaming; that probably explains why we cannot recall Dreams, and why nothing seems to happen in Deep Sleep.
If that observing Being was divine, and was intervening to affect our lives; a Deep Sleep Being could only affect the broad outlines and shapes of our lives, and after a delay; whereas a Being in Dreaming Sleep time would be able to affect many detailed things in Waking life, almost instantly.
If we then consider the purpose of our three states of consciousness, in terms of our mortal lives having the purpose of giving us experiences from which we may learn that which we (personally) most need to learn; it seems likely that Dreaming has a very important role in our lives - because in Dreaming we can experience a far greater range of experiences than in waking life.
Since dream experience feels pretty much the same as Waking experience, but we can fit (say) 100 times more into an hour of Dreaming than an hour of Waking; and since furthermore Dreaming is not constrained by material limitations, but can provide any experience that can be imagined; it may be that most of our experience of life is achieved in the Dreaming State.
Perhaps in Dreaming we get the greatest breadth and quality of experience; but the experience is not as powerful as Waking experience - which is narrower, deeper and simpler; and is dominated by external, sensory input.
And then Deep Sleep provides experiences that are extremely simple and relatively few; experienced derived via inner sources - but perhaps the most powerful experiences of all.
Perhaps - in other words - there is a trade-off between the speed of time, and the depth of experience; such that the three states of consciousness - between themselves, and overall - provide each person with what they need to experience, in ways suited to their capacity for learning.
Note: I think that Deep Sleep, Waking and Dreaming all continue all of the time; to varying degrees - and consciousness moves between them. So, as we are awake, as you read this; Dreaming is ongoing, and also the slow motion of Deep Sleep. For instance' when we 'nod-off' to sleep, our consciousness can suddenly 'drop-into' an already on-going Dream, or the on-going process of Deep Sleep.
The sources of experience, the source of 'content' of these states of consciousness, is likely to differ; although probably this is a difference in emphasis rather than absolute. For example it seems likely that Waking States are dominated by the senses, and perhaps especially vision. Dreams seem to be in the universal realm of consciousness - the underworld, the 'dwat' of the Ancient Egyptians, the realm of what Jung misnames the Collective Unconscious (because it is actually as Conscious as we ourselves are conscious in dreams). Deep Sleep probably derives its content from emotion; that is from our inner world of organs and vegetative functions.
So Dreaming, Waking Deep perhaps broadly correspond to our persepctive on universal reality, immediate external environment, internal environment.