The most straightforward benefit of fragrance free cat litter is that it doesn't introduce any additional smells into your home. Some cats are genuinely sensitive to strong scents and may start avoiding the box if the litter smells too overpowering to them — and a cat who avoids the box is a problem no owner wants on their hands.
That said, scent is only one piece of the puzzle. Clumping quality, dust levels, odor control, and ease of scooping all deserve equal attention when you're choosing.