When a cluster is not configured for failover, by default tasks can execute on any resource group (assuming that the default configuration for resReq and ResourceGroupName is used in Consumer section of the application profile).
When a cluster is configured for failover, by default work only runs on hosts that are not configured to be management hosts (hosts that are not marked with the mg resource attribute). Work does not run on any CPU slot in the ManagementHosts resource group.
For performance or other reasons you may not want workload to run on the master host. It is possible to change your configuration to dedicate the master host as a management host. In this way, you ensure no application workload runs on your master host.