I think there have been some good comments in this thread about why conceding can be a good thing, but I think conceding when playing online has to be handled more carefully.
Consider two possible scenarios in real-life board gaming:
Scenario 1: A player can see that they are guaranteed to lose so they congratulate the other player for their playing and concede the game.
Scenario 2: A player can see that they are guaranteed to lose so they get up and walk off.
Scenario 1 is respectful, whereas scenario 2 is extremely disrespectful and petulant. I think conceding in an online game can easily come across as scenario 2, rather than scenario 1, even if that is not the intention. I've had a number of cases where I am on course to win and the other player simply concedes without making any comment in the chat. This seems very rude to me.
I would suggest that if people are going to concede a game then they should first post a message congratulating the other player, to make it clear that they have not just walked off in a huff.
Consider two possible scenarios in real-life board gaming:
Scenario 1: A player can see that they are guaranteed to lose so they congratulate the other player for their playing and concede the game.
Scenario 2: A player can see that they are guaranteed to lose so they get up and walk off.
Scenario 1 is respectful, whereas scenario 2 is extremely disrespectful and petulant. I think conceding in an online game can easily come across as scenario 2, rather than scenario 1, even if that is not the intention. I've had a number of cases where I am on course to win and the other player simply concedes without making any comment in the chat. This seems very rude to me.
I would suggest that if people are going to concede a game then they should first post a message congratulating the other player, to make it clear that they have not just walked off in a huff.