When fildo both partners file their own taxes but choose the file together option?

No, married partners do not have to file individually.  They can file joint or married filing separately.  

Generally, filing jointly will give you a bigger refund or less taxes due. When you file separately, your tax rate is higher and you won't be able to claim:

• Education benefits
• Earned Income Credit (EIC)
• Child and Dependent Care Credit (usually)
• Adoption Credit (usually)
• The same benefit married filing jointly couples get for personal exemptions, itemized deductions, the Child Tax Credit, and capital losses (all of these deductions are reduced by half)
• The standard deduction if your spouse is claiming itemized deductions

On top of that, if you live in the community property states of Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, or Wisconsin, you have to deal with community property allocations and adjustments, which adds extra work and complexity to your tax preparation chores.