According to cavelamb himself :
DoN. Nichols wrote:

[ ... ]

What is needed there is a limit to the number of articles per
hour that any one machine can submit to the news server.

[ ... ]

Tell me again why cross posting is a necessary thing???

Because it allows a *proper* newsreader to avoid showing the
same article multiple times when it is cross-posted to a collection of
properly related newsgroups (examples for us are
rec.crafts.metalworking, alt.machines.cnc, and
sci.engineering.joining.welding). It is assumed that a certain
percentage of one such newsgroup will read the others as well, and a
proper cross-posting will only show once with a proper newsreader, so
you don't get offended by seeing the same article many times.

In contrast, multi-posting does not offer this benefit.

Also -- a cross-posted article uses less disk space on the news
servers around the world. Unix filesystems allow links which tie
multiple filenames in different directories to a single file, so only
one copy needs to be stored. As it the article expires in each
newsgroup (which may have a different expire time per newsgroup), that
link is removed, and once the last link is removed, the file vanishes
from the filesystem.

The reason that unix filesystem behavior is important here is
that most news servers run on unix systems.

Yes -- this does not make much difference for a single article
in three newsgroups, but when it happens thousands of time over the
hundreds of thousands of newsgroups, it can make a significant
difference in disk space required to run the news server.

To *you* -- it probably does not make much difference -- other
than the fact that if it becomes more expensive to run news servers,
fewer companies will run them. A lot of news servers are run by
companies as a perq for their employees, and some are run by
individuals. (This is how usenet news was spread around long before the
internet became a choice.

Enjoy,
DoN.
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