It’s the only way for a lot of gay couples in conservative countries to have legal rights with each other. Like in America, a lot of gay couples were denied visiting rights when their partners were in hospitals/hospice. That’s one of the reasons why the legalization of gay marriage is so important. Another legal reason would be their child’s custody if something were to happen to the legal guardian. In this case Sol would go to the (legal) “grandfather” Haebom. This would also give the partners the legal right to make medical decisions for each other. It may seem strange, but this is the closest a lot of these couples can get to be able to become a legal family and protect each other while gay marriage is not legal.
There are a lot of benefits that queer couples don't get for example the transfering of inheritance to your partner's name,taxes and bills.There are many other benefits in different countries that is accessible only by a straight married couple.Also the societal stigma is there that makes it difficult for queer ppl to access those areas easily.
It is most important in case of medical emergency or if one of them passes away. Now Ho will inherit everything Kwon has if something would happen to him instead of getting nothing and if something would happen to Ho, Kwon would become Sol's legal guardian instead of Sol becoming an orphan in the system.
Also they will be a family now in the system and Kwon will be related to Sol as well.

Wait I don't get it???? Kwon adopted Ho? How will that be helpful? He's legaly his guardian/father I don't get the point???? Why? Whyyyy