It is not my idea per se, of course… I only gathered (well, it seems sort of obvious) that, given the overwhelmingly social nature of human intelligence, communication with high information throughput is likely the key differentiator between HS and other apes; the rest was ~1 minute of googling.

As to “side effect”, given better communication and consequently cooperation and potential for more complex collectives lead to persistent survival of the species in the environment, they seem like a pretty straightforward evolutionary advantage that would be expected to be naturally selected for in the first place. If anything, chances are in long term the great larynx update is the real side effect, it just happened to be a trait enabling all the above evolutionary advantages.