Most of the time when a designer takes over a new project the first thing they want to do is completely throw out the old and create something new, unique and worthy of their time and grand ambition. I have been in this camp, and it can be a lot of fun… creativity aside, it is also the easy way out. Don’t get me wrong, taking over a half-baked system full of broken shit is not all sunshine and rainbows — more like raindrops and mud-puddles. All of this not withstanding, it doesn’t mean that it is the correct choice. At the very least, it should still be a last resort.
Design revolution, although sometimes necessary, is often a sign of poor planning or no intention. If you need to start from scratch rather than iterate and improve incrementally, it should warrant a complete paradigm shift; Something that the user or audience sees as inevitable in hindsight.
Be cautious. If your brand is new or fragile, it may not survive a revolution. Even branching a brand, as an endeavor to new industries, will require a drastic repositioning, and grand scheme changes are usually accompanied by lose of advocates or champions. Know that with revolution there we be casualties. There will be a rebuilding stage and nothing points to foregone success. It is fraught with danger and littered with failure. This is why evolution is the better strategy.