Downloading my full backup would use the entire month's quota on Comcast, forcing me to pay more money to my crappy ISP.
Downloading rarely makes sense for a full restore, but is perfect for smaller restores or tests. Even if it didn't blow away your quota they only keep the packaged restores around for 7 days and I've found that difficult to restore a large amount of data with home Internet.
To restore it to a drive all you pay out of pocket is return shipping of the drive. The one time I had to use it I was slightly over the 30 days (I was waiting on a repair before I could restore the data) and it wasn't an issue.
At least for the standard Backblaze service you can download for free. For a USB drive you float the cost of the drive (they reimburse you when you return it)--maybe you pay shipping?