Sounds like a good idea to have spares just in case. Isn't that the point!
To have spares ready to replace non-serviceable items immediately seems kind of sensible to me.
Well yes, yes it is. However, for the system to work, those spares need to be visible by the 'system'. There won't be enough of those items for every chief in the RAF to have a few in his drawer, so they need to be kept where those who oversee ALL of the requirements across the RAF can manage their locations and use.
The numbers set are not made up by loggies. They are determined by the engineering specialists and those responsible for the fleets, who are also not loggies.
Overall, the systems used to manage spares etc work very well, when they are allowed to work. Long screwdrivers, meddling, self-importance and the desire to be promoted seemed to be the reasons why it didn't work, and of course Engineers thinking they know better.