These so-called "system optimizers" or "error cleaner", use intentional false positives (fake info re operating system, e.g., registry errors, disk junk, etc.) to convince YOU that your systems have (non-existing, misleading) problems. (Once installed) Then they (just) try to sell you their software, claiming it will remove these problems (only when you choose to give some money to 'em). More information can be found on this Malwarebytes Labs blog post.
Last but not least, they are really yet another forms of PUPs or FakeAlerts.