Most of the truly obnoxious on usenet have such groups. Most ISPs include the above mentioned header. .
Resistance is useless.
As a way of coping with floods and the like it does work and I have used it that way. Another thing to consider is that UUCP sites and some other software do not insert a NNTPetc header in the article. However in the yarn either global or newsgroup score file it is highly practical and is used by me. However, scoring is like stew making, you have to decide for your self if the flavor is enhanced with possum liver or not.