Here's the condensed version. At the start of a war, coordinate several of your armies, if possible, so they all arrive at enemy provinces during the same month. Set your budget slider to take all cash to treasury, then at the end of the month you get a full year's tax, in cash, from every looted enemy province. Then reset your budget slider back to whatever you normally invest in. You get a pretty good amount of cash for a cost of just one month's inflation (i.e. .083%), which is really a good deal. If you have a small country near the beginning of the GC, just looting 1 or 2 rich provinces can make a huge difference in your cash flow.
Once looted, a province cannot be looted again until the city icon stops burning, which is 13 months. During that time, the owner gets no tax income from that province. That includes the annual census tax, and be careful because you can lose tax money the same way to enemy armies or rebels.