This article is from the Digital Broadcast Satellites FAQ, by Brian Trosko firstname.lastname@example.org with numerous contributions by others.
Crossposting can be a valuable tool for getting your message
to the maximum number of people. It can also cause a discussion
to degenerate into a senseless flamewar. In general, you should
only crosspost a message to several groups if it is really and truly
relevant to all of them. Contrived reasoning does not make a message
relevant. For example, news that a DBS program provider will soon
be providing the WGN superstation out of Chicago would probably
be relevant to r.v.s.d, r.v.s.misc, and possibly even r.v.s.tvro; readers
of all three groups would probably be interested, but many interested
people probably don't read all three groups. But it would not be
relevant to alt.sports.baseball.phila-phillies, just because the Phillies
play against the Cubs, and the Cubs are on WGN.
There is one special caution about crossposting. Be careful when
crossposting articles between rec.video.satellite.dbs and
rec.video.satellite.tvro, because flamewars between proponents
of the two radically different systems often burst out, and can drown
out normal discussion for days at a time.