Why double-spool print jobs?

[John Ruckstuhl]

We have commercial electronics design software, Valid, running on Suns.
This SW insists on double-spooling plotter jobs.  
    Does this make sense?
    Is this a common solution among SW products?
I don't see the necessity or advantage.

>From the Valid Guide to Operations explanation:
    The /etc/printcap entry for (application-specific-pseudo-device)
    instructs lpd to run the (application-filter) on the data.

    The (application-filter) transforms the input data into a format
    acceptable to the plotter and calls lpr with the -Pplotter-name
    option to sent the formatted plotter file to the correct directory
    for the type of plotter specified.

    Another daemon then spools the plotter-specific files to the
    plotter.

    The double spooling allows other programs to access plotters in an
    orderly fashion, and keeps (application) users from having to wait
    for their plots to be processed.

Can't one achieve the same effect, and wouldn't it be cleaner, if the SW 
just sent the data directly through the application-filter to the print 
spool in the background.

Thank you for your comments.
Best Regards,
ruck
-- 
John R Ruckstuhl, Jr			ruck at alpha.ee.ufl.edu
Dept of Electrical Engineering		ruck at cis.ufl.edu, uflorida!ruck
University of Florida			ruck%sphere at cis.ufl.edu, sphere!ruck