Well I'll throw my two cents worth in.
1)They are not neccessary in writing a message and could even go to the
extreme of poor style.
2)However for field biologists they are extremely neccessary. Here a good
example;
Its that time of year again and I was doing Point Counts down at Nisqually
NWR this morning. When I've only got 5-10 minutes to do a point and I have
anywhere from 4-9 species on that point, I would go mad trying to write
Orange-crowned Warbler, Common Yellowthroat etc... not to mention it would be
a huge filler of field forms. Its much easier to write OCWA,COYE etc..
So yes 4 letter codes have very important roles, mainly in field notes and
field biology. They are not useful when communicating to the genral public
though. This is why they are probably not appropriate for tweeters.

Scott Downes
sgd24 at aol.com
Seattle WA

To identify a species should not be enough to quench one's thirst,
a proper thirst must seek to understand every facet of the bird's
existence.