Having sex-disaggregated data is the only way to build consistent tax policies
The fact that governments have access to non-sex-disaggregated data means that they will never be able to take decisions that guarantee gender equality. This is true for how we define GDP (see: calculating the gdp of a country should include the unpaid work done by women), but also for how we design tax schemes. There is evidence that one filing joint tax declarations, the lower earner is prejudiced, and since normally those are women, in the end it turns out that filing join taxes is detrimental for women [@criadoperez2020Invisible women: exposing data bias in a world designed for men]. There are many caveats to that assertion, but it works for taxes which are bracketed, such as income tax.
Designing schemes that benefit the wealthy also tends to benefit men more than women, or corporations which are owned and manage in their majority by men and not women. All these, in principle, gender-neutral actions tend to be more in favor of men than of women and therefore they keep piling up over the years. It all comes down, on the one hand, to the gender data gap, but also the having leaders that do not represent society in its conformation.
This can be shown by looking at expenditure patterns in the UK after the government (in the 70s) decided to transform child allowance from a tax break (which benefits mostly men) to a cash payment to the mother of the child. See also allocation of resources in a household is not gender-neutral.
These are the other notes that link to this one.