It is up to the resource owner to define a policy for when Condor requests will serviced and when they will be denied. These people want Condor to provide as many CPU cycles as possible for their work. Often the interests of the resource owners are in conflict with the interests of the resource requesters. The job of the Condor administrator is to configure the Condor pool to find the happy medium that keeps both resource owners and users of resources satisfied. The Different Roles a Machine Can Play Every machine in a Condor pool can serve a variety of roles.
Most machines serve more than one role simultaneously.
Certain roles can only be performed by single machines in your pool. The machine is the collector of information, and the negotiator between resources and resource requests. These two halves of the central manager's responsibility are performed by separate daemons, so it would be possible to have different machines providing those two services. However, normally they both live on the same machine. This machine plays a very important part in the Condor pool and should be reliable.