I mean, there’s no real intuitive correct answer, so that’s easily forgiven!
The word ‘rail’ is often used with respect to power, and I think it’s a useful way to think of things: what voltages do I want on-demand, everywhere? So in Eurorack, that might be +/-12V, as our range for powering things like operational amplifiers. We might also want a 5V or 3.3V supply for microcontrollers, or perhaps as a gate standard. And then everywhere we want that, we can just tap that rail - and those are the sort of things we used fixed regulators for. By contrast, if there’s a single place a single thing is required - as part of a circuit - that’s where you might see voltage division.
(If you need a highly precise voltage, ie, to several dp of precision, that’s where ‘precision voltage sources’ come in handy - you’ll see these in ‘precision adders’, which are useful for interacting with V/Oct signals).
