So that the customers can configure the Bundle product by selecting custom options before purchasing.
Whereas for the Grouped product there is no feature as such. The seller simply adds the products to the grouped product and the Grouped product will be available on the front end for the customers.
It totally depends on the requirement. If the sellers want their customers to customize the color, size, etc of the Bundle product before the purchase then Bundle Product is the best solution.
But in case you want to restrict your customers and don’t want them to customize the Grouped Product package, then you can go for Grouped Product.