There's been a lot of research now showing that psychedelics probably promote neural plasticity through neuritogenesis, spinogenesis, and even limited neurogenesis (in the hippocampus or something?). I think this is why psychedelics seem to hit the "reset" button, give you fresh perspective, and can get you out of a rut. They put your brain into a more plastic state: open, pro-learning, they turn on your brain's ability to rewire. They thaw out the crystallized pathways in your brain somewhat (habits, reflexive behaviours, default perspectives) and give you a chance to move them to a more productive/beneficial route. From the previous local maxima, to higher local maxima. I think we've all observed these characteristics anecdotally and subjectively - to put it much more simply, that psychedelics can make you a better person. For a few years now research has been showing a physiological counterpart to these characteristics, and to me this validates (to some extent) what we've been suspecting and hoping was true - but sometimes sounds like fanciful hippie thinking.
Anyways, that was a long-winded way to say that microdosing and mini-dosing might be a good way to tap into a steady flow of a gentle mental loosening, learning, directed re-wiring. Rather than tearing the whole house down with the kind of heroic dose trips that make you question the very fabric of reality, these smaller doses are a more practical way to just loosen up preconceptions and soften your brain into being more open to learning again. A series of nudges, instead of an atom bomb.
As we age, our brains tend to get more hard wired and fixed. Our brains prune less-used pathways, and reinforce the most useful ones. This is how training and learning work, and you definitely want this - it's how you "never forget how to ride a bike". But on the flip side it means we can get stuck in some un-useful or outdated perspectives even as the world around us is changing rapidly. Or for another example, some people can get caught in cycles of self-reinforcing depression, as the grooves of depression get more and more well worn in the mind.
To me, taking psychedelics is a way to hopefully age more gracefully, to keep my mind a bit more young and flexible and creative than it might be otherwise. I think a little bit of microdosing here and there might be useful for that, as well as mini doses and more occasional full-fledged trips.