If you don't have to add a dedicated chip to the design to accomplish a task, then you save money -- BOM cost, board space, power-supply, etc.

So if the processor can manage the task without otherwise impacting anything else it does, then leave off the specialist chip.

If your processor is very busy and can't manage the new task, then you have no choice in the matter.

oh, you do, a more powerful processor :)

Erik