Better to have NI 1970s body armour and 1992 desert DPM than none at all. And because much had been got rid of because of RAB, many personnel famously went without both during Telic.
Better to have retained a few spare PR9 noses to avoid the critical situation with regard to pressurisation cycles that we're now facing, or spare engines for the Canberra T4 (they can only fly one T4, 'cos they only have two serviceable engines).
And the list of examples goes on and on....
The Forces exist in order to react to unexpected and unpredictable contingencies. Trying to apply RAB rules to such an organisation is barking.