When you file married filing separately there are certain credits that you become ineligible for. Another important point is that if one of your itemizes the other has to itemize also, which can create a larger taxable income for the spouse that doesn't wish to itemize.
In most cases you will not be able to take the credit for child and/or dependent care and the amount you can exclude if you get dependent care benefits on your W2 goes down to $2500 from $5000. You will not be eligible for the earned income credit, any education credits including credit for tuition or student loan interest deduction. In addition your standard deduction goes from $27700 down to $13850.
In general, filing separately from your spouse results in higher tax liability. There are specific situations where it is done but it generally results in a less favorable tax outcome for you because your tax rate is high filing separately than filing jointly.
People with student loan debt trying to qualify for income driven repayment plans will sometimes file separately from their spouse for that reason, regardless of the tax outcome. That is a specific situation where the consideration is the total income and not the tax rate.
