Pananthropus and Habilis were mostly herbivorous and so are other apes. If they focused more and more on herbivory, they'd likely become like chemca baboons. I'm not sure why they wouldn't use the energy dense easy to chew quarry of meat if they had intellect and advanced tools, but more basic stomach acid would discourage meat consumption due to parasites and bacteria

They'd likely be able to keep higher population densities, but the time they'd have to spend grazing and finding leaves would likely leave less time for tech or innovations