This.
Accurate data on who commits how much of which types of crime are important - for prevention, for detection, for ensuring the correct proportions of different types of prison are built etc
And one of the many arguments for keeping men out of women's single sex spaces is their much higher propensity for violence. If men commit vastly more violent crime and sex crime than women, clearly they pose a high risk. So putting them in a women's prison or allowing them into women's changing rooms and refuges would be a daft idea. If half of these crimes are apparently committed by women, the clarity of that argument is reduced.