This controls where SCM polling is performed.
If this is not selected, SCM polling will be performed on the agent that handled the latest build.
If this is selected, SCM polling will be performed on the controller. This allows polling to be done even when no suitable agent is present; a prerequisite when using on-demand provisioned agents. However, the Plastic SCM command line client must be present and configured on the controller.
Note that Jenkins stores this setting at each build, and SCM polling uses the setting from the latest build. Changes to this setting will only take effect after you also have triggered a build.