If using multiple screens at work made you more productive, care to give an example or two what do you put on one and the other and how they interact? Perhaps also negatives, in what situations that doesn't help?

Hypothesis: they only work with transformation type work e.g. translation where you read a document in one and translate in another, or read a spec in one and write code to implement it in another or at any rate the output you generate is strongly dependent on an input that you need to keep referring to.

I actually borrowed a TV as a second screen because I need to re-create the layouts of document reports from an old accounting software in a new. So it is handy to have the example on the TV while I work on the new one. Of course a printout on a music-stand would work just as well...