The .vmsn file only contains the VM's latest configuration and - in case of a powered on VM - its memory state. With each snapshot you take, the current virtual disk file (.vmdk) is treated as read-only and a new one (or multiple, depending on the virtual disk format) is created for changes/writes. All the snapshots are then used as a chain, where each chain link contains data.
Although VMware KB: Understanding virtual machine snapshots in VMware ESXi and ESX describes snapshots for ESXi, it's worth reading as this is similar for VMware Workstation.
André