CleanMyMac is crapware. Crapware is anything that purports to "optimize", "clean", "accelerate", "monitor", or "protect" your Mac. These apps are unnecessary, poorly written, overpriced (if they were free, they'd still be overpriced), and harmful. They can damage your OS and be difficult to uninstall. But, some people really like crapware. That's why the a-holes who sell this stuff sell it- people keep buying it. New Mac users and converts from the PC world need to develop crapware detectors.
The king of crapware is MacKeeper. CleanMyMac is a close second.
Third-party antivirus software on Macs is not crapware, but is of minimal benefit. Macs are not PCs. Macs have anti-malware protection built in already.
I used to use ClamXAv and then Sophos. Both started running away with CPU usage and slowed my macs down. They never seemed to find any actual malware, but were good at finding false positives. So I stopped using antivirus software about a year ago. My macs have never run faster or better or more reliably than they do now. I keep up with Mac OS and security updates, I have good passwords, I am careful what I download, I do regular backups, and I don't think that Nigerian bank presidents want to make large deposits into my bank account.
I understand the point about not wanting to transmit Windows viruses to my PC using friends, but most of the people I communicate with are Apple people anyway, and the PC people are smart enough to have their own antivirus software.
If people really want to have crapware and third party antivirus software installed on their Macs, then maybe a PC would be the way to go.
<Edited By Host>