Doesn't anybody remember the "Whack-a-Mole" children's arcade game? They give you a padded mallet, and you stand in front of a table filled with fist-sized holes, through which mole-head puppets pop at random intervals. Children (well, my children, at least) seemed to enjoy floundering around with a blunt instrument aiming at moving targets. Parents appreciate the blunt instrument being padded, and the moving targets not being other children for a change. A sure-fire winner, endless fun for all the family.
There's something about some categories, or maybe it's the kind of people that create certain kinds of sites, that brings out the "if one submittal is good, two are better, and a three-ply cord is not easily unspammed" school of delusional fantasy. Ineffective, and counterproductive it is: because ... trust me, editors have seen it before.
So if, say, I don't feel like reviewing actual sites, but I want to do something constructive, I have my list of categories where the moles are sure to have been busily tunnelling, take up the mallet, and go after the duplicates. It saves some other editor (who's looking for actual sites to review and list) time, and it's something constructive you can do without much of a functioning brain.
Looking at it from the other side of the arcade table (the webmaster side): After a certain variable number of whacks (probably between 5 and 50) a site becomes an official garden pest and therefore an endangered species. Two or three dead mole pelts on a site's door are too common to excite notice among editors, but it is time for submitters to get really careful...like, break that submittal habit, remember to NOT submit any more, but remember TO check status periodically.