In essence, VSS provides improved support (UK phone number) and free upgrades as and when new versions are released. VSS can be purchased on both new Vectorworks licenses and upgrades. Most users choose VSS to ensure they are running the latest version of Vectorworks, with all the latest features, without being caught paying a lump sum every couple of years to upgrade.
VSS is a 12-month subscription. You are asked if you wish to renew at the end of the 12 month period.
Currently, new licenses are eligible for 50% discount on VSS. On upgrades purchased with VSS, a 25% discount is available on the upgrade itself (the VSS is sold at normal price).