You take the ones you aren't going to use or use any time soon (especially the dead-ends on the tree) and when you are one turn away from getting them, you switch to research a different one. Save the ones with a single turn left for when you want to make a quick free policy switch.
That's interesting. I believe what you quoted was in reference to anarchy from switching governments, which isn't quite the same as switching policies. But a cool idea to save gold!