Currently QuickBuild has the notion of Resources, although these are directly linked to nodes. It appears the linkage is there to allow a configuration to select a node based upon the various selection criteria it has.
Unfortunately, there are times when a logical resources is required, one which is not linked to a node. Consider the case where a configuration must run on a particular node (e.g. due to OS requirements), but it also needs to utilize another set of hardware. If this particular hardware is tied directly to another (single) node, then the node selection criteria can never be satisfied as there are no commonalities.
In this case, a logical resource is required, one which doesn't contribute to the node selection, but rather acts as a simple reservation marker. If the marker is taken, the configuration cannot run, and hence must be queued.