The only reason to regularly clean the glass is if you will want to see through it (front pane, keeping backgrounds visible, etc.) or if there's something "bad" growing on it that you're trying to knock back (cyano, hair algae, etc.). If there's an area you're certain you'll never need clean and you don't mind the look of stuff growing on it, there's no need to break out the scrubber there. Just be sure you'll never need it clean before you decide to skip regular maintenance and let it grow. Otherwise, aside from the huge amount of work involved in scraping off layers of coralline, you may find yourself faced with having to choose between cleaning it and killing animals that have settled there. For one side pane of my 55gal, I made the mistake of saying "oh I'll do it next week" for a couple of months. The day I went to get a scrubber, I discovered a 1" encrusting clam had grown there. I can't move the clam without killing it, so now I have to live with a mucky circle on that pane around the clam lol.