The partner cannot legally made the important / life saving decision the best of his/her interest at the time of emergency.

For instance, when 1 of you got into accident or experience mishap which leads to emergency medical procedure / operation, you are unconscious hence cannot authorized the procedure by yourself. Your partner are in no position to place his/her signature to authorize the emergency procedure.

If Im not mistaken, you cant name GF/BF as beneficiary of life insurance in malaysia.

Not too sure, but if claim inheritance i think 'will' quite powerful, even more than marriage cert. I think the court will layan the 'will' > marriage cert. Lawyers will suggests you to do it, but not sure it's just because they want cari makan. But they say if no will, other parties such as children and parents have a percentage of what the decease leaves behind, if they choose to dispute, if no dispute then no issue.

But, maybe, for kwsp/perkeso/insurance, cert > will. Kwsp has nomination, but perkeso, the checklist is marriage cert to be entitled for it's benefits, as it's for "spouse and children". Not sure if a will can replace a cert in this case.

reason not to sign a legal marriage paper