Japan may be the country that invented karaoke but South Korea made it a point to use it as much. In a hard-working society, letting go and having fun is essential. So, if you are on a business negotiation with South Koreans and are invited to a Noraebang night (the Korean karaoke), complete with heavy-alcohol consumption, by any means, do not refuse, unless you want to lose that deal and you’d better sing! This social occasion is an important part of trust-building in Korea, a way to advance strong relationships between business partners.
Some would say that because your business partners have seen you as few other people have (badly singing, maybe inebriated), you have “no more secrets to hide”, thus strengthening mutual trust. But more seriously, in this more relaxed environment, your Korean counterparts may use this social event as an opportunity to convey important messages or resolve disputes.