If you point it at a TeamCity instance (with the REST API plugin installed), it will randomly select a build and run it.
The idea is to make sure that all builds get run reasonably regularly, and avoid the unpleasant surprise when one that hasn’t been run for 6 months explodes in your face.
(At the moment it won’t run builds with “Live” in the title e.g. “Deploy Foo to Live” (because I’m a chicken :). But really these should also be run regularly, even if the code hasn’t changed).
It would be better if it was biased towards builds that hadn’t been run recently, but I’m not sure if the TeamCity REST API provides enough data for that.