ppl on here say things like “my dhs wage pats the mortgage and council tax and mine pays the other bills” it’s the same thing!!
I'm not sure it is the same thing. I pay mortgage and utilities etc. DW moved in with me, all the bills were in my name, I couldn't make her pay them if I wanted to. She knows I'm not going to refuse to pay the bills just because she doesn't want to contribute. Similarly, she pays for all things child-related. It's not that I don't want money spent on DD, but I know if I pay nothing, she will.
OK, we're an extreme case, and I take no responsibility for our fucked up relationship, it was her idea to from the start treat me as an adversary to be taken advantage of rather than a partner to come to agreement with.
My point is that different people paying for different things has more complex and different explanations than one person compartmentalising money they have complete control over.
I don't think it's logical to link the grocery budget to the child benefit payment, but if the two happen to be the same amount, then there's no harm in it, for as long as that remains true.