Full Disclosure: I worked on the physical security of the Snowmobile when it was originally introduced, it was a really fun project.
The idea of the Snowmobile was to enable gigantic transfers of data, in the case of the first customer it was a GIS company with a data lake of 20 years of archived data. They built a fence in the parking lot next to the loading bay, ran some serious fiber to it, put in a bunch of cameras, and Amazon brought a cargo container full of racks of drives and parked it there. They then spent the next six weeks transferring their data to the Snowmobile (breaking their backup tape library three times in the process) while the AWS SOC continuously monitored the security of the container and their onsite security monitored the data line. Then Amazon hooked up the tractor, drove it to Portland (again continuously monitored by the AWS SOC), plugged it into the PDX data center, and over the next couple of days moved it all into their racks. Within a week the customer was offering products that their former configuration hadn't allowed.
The customer had estimated that transferring that much data via the fastest available connection would have taken 3 1/2 years, assuming no issues (as if that has ever happened). My understanding is that the Snowmobile was originally envisioned with the Pentagon in mind, as they have entire data oceans of GIS data currently stored on systems so old that they're buying parts on (literally) eBay. Today the Snowmobile is outdated, as a petabyte of data can now fit in a carry on suitcase.