This is to cover for cases where the person in question is not receiving the Child Benefits (e.g. their partner is), and to better reflect on the marginal tax rate in this scenario.
Possibly worth having HICBC in the deductions table, and Child Benefits in the "You keep" table. They are now listed both in "You keep" table, because Child Benefits - HICBC is always less or equal to 0.
This is to cover for cases where the person in question is not receiving the Child Benefits (e.g. their partner is), and to better reflect on the marginal tax rate in this scenario.