Trying to distinguish the difference between "Resources" and "Actual Resources" in UAF 1.2

Trying to distinguish the difference between "Resources" and "Actual Resources." Actual Resources in UAF 1.2 refer to actual resource configurations but do not support relationships like "Implements" like Resources do. Is there a method/rule on why? It seems to make sense to be able to use the same relationships for Actual Resources to create traceability between activities and such.