Goosefoot interesting points, ime it's not necessarily linked to state benefits, if that was the thing you were thinking. Lots of people are id'ing into groups not seemingly with the intention of gaining anything from the state.
No, that's not quite what I was thinking, although sometimes that happens, particularly with parents wanting to get services for children or accommodation in schools. Even f there is clearly a problem, without a diagnosis there is no basis to ask for certain programs or resources.
My thought here is more on a conceptual level. Because of the way we've understood discrimination, or disadvantage, it's become very difficult to make claims of being disadvantaged, which the state must address in some way, unless you can make it some form of identity claim. For example as a woman, I can point to my class being most at risk of sexual assault, or differences in lifetime earnings, as examples of disadvantage to my identity group, and demand policy actions, or programs, to address these problems. I may or may not get what I want but the claim is understood on both sides to be a valid form - women should be equal to the comparison group (men, in this case) and where they aren't, the state has a responsibility to address the gap.
It's quite different than my personal disadvantage through luck, or my particular family history, or whatever, even if as a result I am much worse off than the average woman compared to the average man. As an individual with individual circumstances I have no claim to the state's intervention into those circumstances.
We could divide people up into hundreds of possible identity groupings of course, that have long term effects on people's circumstances, but ultimately the ones that count are the ones the state recognises, or the ones groups can convince them to recognise.
I think there are a lot of fall-our effects of this. People have significant motivation to see themselves as part of a state recognised grouping, or convince the state to recognise it, and to show somehow that they are disadvantaged as a group so they can make claims to programs, policies etc. (This gets into interesting questions about who they compare themselves to.) And that tends to spin-off to other forms of intervention as well from non-state groups. The state potentially has a lot of power here, as well as those best able to make their case for their group - it's in their interest to support the power of the state rather than to challenge it.
I think it's become increasingly difficult for anyone to claim that the state should look at their problems without putting it in terms of an identity group that's been disadvantaged compared to the norm.