My two cents.
Repeated low dosages seems to create a lot more physical side effects in terms of hallucinations while not on psychs and generally fits within a slow transformation model, whereby to some extent you are tripping slightly all the time. There was a time period of nearly two years where I would never even see blackness while shutting my eyes - but rather an explosion of colors, faces, forms, essentially instant dreaming with just the lack of direct visual stimulus.
High but infrequent dosages, meanwhile, never seemed to have the longterm aspect associated with them UNLESS there was some vastly significant mental breakthrough (whether for good or ill). This is more mentally based, however.
That explanation sucked. Maybe I can explain this better more technically.
So for example, large infrequent doses are less likely to create the "permatrip" - defined by the brain learning to frequently use certain mental pathways associated with the trip experience. The constant use of these pathways even at small doses becomes a neural habit, and therefore you are more "permatripped" as a result. However, large doses will create imprint vulnerability. This means, if I imprint "smoking is bad" "I should be a more caring person" or "demons live in the alley outside my house" that imprint is more likely to stick - just because that's how our memory defines itself in such a vulnerable moment. Even though it might not stick in terms of a psychosis or compulsion, I might suddenly not crazy cigarettes as much, or I might find myself unduly nervous every time I walk by that alley. The repeated low doses can potentially cause your brain to be conditioned to certain ways of thinking (including hallucinating). The high doses, if infrequent, are not going to cause this learned behavior, but could potentially trigger an imprinted mental phenomena.
My experiences.