If you offer free shipping for more than a certain order value, it can be helpful to show a message in the cart to tell the customer how much more they need to spend to qualify for free shipping.
If a product has no price or a price set to zero it shows as price 0.00. It can look much nicer to have it shown as FREE.
When you have a number of possible shipping options available but one of them is free, there is no point making your customer choose between them. This code hides any paid options when free shipping is available.