There are a couple cases where if you both make similar incomes, filing separately is the better case (but beware certain restrictions like how you can't deduct student loan interest if you file separately)
If you look at the tax brackets:
Tax Bracket Married Filing Jointly Single
10% Bracket $0 – $17,400 $0 – $8,700
15% Bracket $17,400 – $70,700 $8,700 – $35,350
25% Bracket $70,700 – $142,700 $35,350 – $85,650
28% Bracket $142,700 – $217,450 $85,650 – $178,650
33% Bracket $217,450 – $388,350 $178,650 – $388,350
35% Bracket Over $388,350 Over $388,350
if you both make 75k each, then if you file singly, you both stay in the 25% bracket, but jointly you would bump up to the 28% bracket for a small portion of your income. In this case filing separately would save you a little bit of money.
But as you can see, that only applies if you both make between 71k and 85k or both between 109k and 178k. In just about all other circumstances, filing Jointly is a better deal.