Every time I do a water change my decor changes a bit. a rock moves from here to here, let's see how this looks for a while, and so forth. I don't do a full deliberate change unless I'm taking something out of the tank.
When I do a water change some plants get torn out, some were eaten by a fish and I want to tear them out. I add some plants from time to time too. So about once or twice a month, but only during the waterchanges.