Most problems Mac users encounter today are due to 3rd party utility cleaners, anti-virus, and other tools that they really do not need. The second largest problem is not buying enough storage on a modern Mac. The last problem is adware / malware which is less of an issue. Previously, it was prior to SSD and APFS. Even worse before HFS+ Journalling where file system corruption was a serious problem.
If you only install software from the Mac App Store and you don’t pirate software nor browse the seedy underbelly of the Internet and don’t fall for phishing attacks. Then you won’t have any major problems unless your hardware begins to fail. If you do install 3rd party software, ensure you are downloading it from the official website and that you trust the vendor. There are many bad actors posing as legit software. i.e. MacKeeper is legit albeit poor but there were half a dozen impersonators and that is true for Clean My Mac. Don’t click on advertisements nor SPAM emails to install this software many are the impersonators. Go directly to the official website instead.
As to Clean My Mac, emptying user caches is not necessary and does in fact slow things down or could break an App in some rare cases.
If you are running security tools make sure you check if the version you have is compatible before you upgrade to the next major version of macOS. Consider enabling automatic updates on 3rd party software most offer it. Many people experience considerable pain upgrading to the next major macOS release because they failed to check their security endpoint software which may not yet have been upgraded to smoothly handle the changes Apple makes to macOS. Or they failed to update it before they upgraded the operating system. It is recommended to wait at least 90 days after a major macOS update or until Apple has released 2-3 dot release updates to the new version before upgrading. Upgrading day-one is very risky.
The last several years, Apple has been making radical changes to improve security on macOS. This has resulted in a great deal of work for corporate enterprise customers running advanced security endpoints such as Crowdstrike, data loss prevention tools, mesh VPN software, etc.
Many people have a half dozen tools installed that all need to be checked for compatibility before making the leap to a major new release of macOS. They end up on the Apple Discussions community support forums every single time. Had they upgraded these 3rd party Apps prior to upgrading macOS they may not have experienced rather serious problems. The alternative is to uninstall these apps, especially if you are not truly using them.
A clean installation is something that some people should consider if they’ve been upgrading a Mac for several years. Starting over with a data backup and re-installing your applications offers the opportunity to prune out all the cruft that Clean My Mac claims to fix but doesn’t fully cleanup. At least not a pristine state.