Some people call gg'ing pointless or empty - plenty of etiquette is pointless and empty.
We do it anyway, because spending a minimal amount of time and effort to be polite is a decent thing to do.
+1!
It doesnt really matter if it was a "good game" or not. imo its basic courtesy saying "ok the game is over, well played, good bye!" all in two letters. Basic etiquette like in Australia you say "how are you" or "hows it going" every time you meet someone. Did you know in Singapore especially for the non-professional (students, part time jobs etc) population if you say that people look at you weird or don't know how to answer? Its just not being said much in our culture, people just say "Hi" and thats that lol!
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