Well just look at their charges for boxing things for you. That's how they make their money. Service fees.
Also note the rates and the weight cutoff for each. For an example, I shipped a box to canada last week via USPS. At first I used the original box they sent me. Super dense and heavy box. Came to 5 lbs and $55 for first class shipping. So I used a different box but some of the same balled up paper he sent me. 3lb 3oz. and $35. So I replaced all the balled up paper with packing peanuts. Weight was 2lb 15oz and cost was down to $25. Every ounce counts.
I know they suck for the environment but I keep all packing peanuts I receive in a huge box and reuse them. If we reuse them over and over they dont end up in the landfills or floating down the street in a light breeze. But also, importantly, they save you money.