Generally, shareware is a kind of proprietary software, which is provided to users without payment on a trial basis and is often limited by any combination of functionality, availability, or convenience.
MacPaw’s CleanMyMac Classic is a shareware program. This means that you can download CleanMyMac Classic for free, however its functionality will be limited until you purchase a license. To be more precise, a free version of CleanMyMac Classic allows you to conduct a complete scan of your Mac but clean only up to 500 MB of unnecessary data.
Only after purchasing a license and entering the Activation Number in the activation window will you be able to keep your Mac completely clean. After activation, there is no size limit to the amount of unnecessary files CleanMyMac Classic can clean.