Expanding a little on Snow's answer:
Many organisations take an interest in the diversity of their workforce, with dimensions such as race, age, gender, transgender status, orientation, parent/carer status, and disability being among those that are commonly examined.
This can be for a variety of reasons, e.g.:
- Some research indicates that diverse teams make better decisions, so organisations may see this as something to aim for.
- Organisations that are concerned about the risk of e.g. discrimination lawsuits may want to know whether anything in their hiring processes is leading to inadvertent discrimination, and may want to be able to document the kind of applicants they get.
- Some organisations, in particular government and non-profits, may have a mandate to meet targets for representation of certain groups. For example, the Australian Public Service has/had a target of 3% Aboriginal/Torres Strait Islander employees by 2018.
Depending on local laws, it is often illegal to discriminate against individual candidates based on their responses to these questions. As a member of a recruiting panel, I don't see whether a candidate has ticked those boxes. But it can still be very useful for an organisation to understand the overall demographics of their applicants.
For instance, let's suppose that in a given year, my organisation hires 90 men and 10 women, and we have concerns about that imbalance. Is it because we're just not getting many women applying? (If so, we might need to look at how we're applying - perhaps it was a mistake to rely solely on ads in Beard Care Magazine?)
OTOH, what if we're getting roughly equal numbers of men and women applying, but the recruitment panel keeps selecting men over women? If so, we might want to look more closely at how the recruitment panel is making that call, and whether the process is as merit-based as it's meant to be.
Getting demographic data about your applicants helps distinguish between those cases.