An exception to this is when you want to build up your economy - low taxes gives quite a large boost (well, reduced penalty) to town wealth growth. I found as Shimazu, when I had conquered the 2 southern islands and was preparing for realm divide, that this helped boost my economy significantly, as I was pulling in so much cash already that I couldn't spend it. Of course, I was probably turtling far too much, but that's another discussion.