Where does / doesn't a JD index system shine in a knowledge workers personal library?

I am avoiding software discussion at the moment partly to understand at a conceptual level, and partly because of my own tendencies to go down rabbit holes - and also, under the banner of combination, push tools beyond their natural or appropriate boundaries.

Here’s a separate list: Current tool set

Why digital? Slip of the pen, really - or maybe because some (of my) reference books are not digital, though almost all are – and because I’m not talking about an insurance style of inventory, but rather stuff I use to produce or enable work.