So as the other comments are going to say, this doesn't work because of noise and linearity issues, temperature sensitivity etc. But there is one place which is trying to bring this back: there have been attempts to do analogue neural networks, where getting the exact value isn't so critical and the system has a certain amount of noise correction by its very operation.

The last greatest flight of pure-analogue control systems was Concorde!

(There are a few places where multiple signalling levels are widely used; things like MLC flash and some of the faster ethernet specs. I don't think anyone's dared to do arithmetic on them before quantizing to digital, though.)