here is the point, Yes, a CP can use the support money to pay the entire rent bill, thier visa card, thier trip to aruba, the new boiler in the basement, the RV, the civil war chess set, etc......
as an example, if you could depend on support to pay your rent, or mortgage, that would be great because then any money you earn can be more freely spent on your kids, because you have used some of "thier" money to pay your portion of 'your" rent, right? (a quick search of apartments will tell you thier is usually only a couple hundred difference, in 1-2 bedroom apartments and 3 bedrooms)
Once child support leaves the NCP's hands, its for the CP to decide how they add it to thier household income. And the NCP is no longer obligated to provide anything more financially for that month.
child support is designed to encompass, ALL the expenses involved in raising a child, from housing and food and healthcare, to extra curriculars. School lunch and uniforms, field trips, little league,are not considered extra's as they come under the basics.
Major expenses to be split, aside from suppport, MIGHT be things like private school, if the child already attends, expensive sports (hockey, horseback riding) if the kid already takes them. major medical expenses if the kid already has a condition, etc.....