I am not sure what you mean of " apart from the spouse"... living apart from the spouse and proceeding a divorce? Or just different meaning in Chinese...

As long as your family structure is simple, say, you are married and have several kids, it is ok to leave it blank. When you don't name beneficiaries, your IRA balance will be paid out in the following order: to your spouse, children, grandchildren and then to your estate.

When things are complicate, in order to avoid unnecessary prorate costs and unintended tax burdens on family members, it is always the best to have beneficiary designation on file... ( for example, I had a case of a divorced lady with an adult daughter. She recently remarried. She has her own living trust...Instead leaving the IRA to the new husband by default , She wants to leave it to her daughter , then the living trust... See? )