The data structures in this case are typically persistent, complex, and large scale - the subject of general purpose applications, as opposed to specialized processing of specialized data sets seen in high productivity applications (HPC).
The model allows the creation of large scale applications that partially share common data sets.
Programs are functionally decomposed into parallel processes that create and act upon logically shared data.
The paradigm is likely to appear on desktop computers as microprocessors increase the number of processors (multicore) per chip.
The Actor model might usefully be described as a specialized kind of process-oriented system in which the message-passing model is restricted to the simple fixed case of one infinite input queue per process (i.e. actor), to which any other process can send messages.