Why a week? In a nutshell, that's how long it takes your Mac to collect enough system clutter to slow down your everyday tasks.
But luckily, after years of work, we do have some universal recommendations. We believe the best way is to experiment with CleanMyMac and, with time, figure out your own schedule. How often and how extensively do you use your Mac? What's the size of your hard drive? Which applications do you use? Do you install updates regularly? With so many questions, it's hard to give common advice. There are no strict rules on how often you should run CleanMyMac to keep a computer in good shape.
