CCleaner Professional includes a system and browser monitoring feature allowing you to set CCleaner to run in the background, so your PC is always optimized. With the monitoring feature you can clean your PC whenever a) you close a Web browser, or b) it detects that it can recover more than X amount of hard drive space.
For example, if you're concerned about privacy, you can tell CCleaner Professional to wipe browsing history, temporary files, and cookies every time you close your Internet browser.
If you want to keep your PC running smoothly, you can tell it to check for unneeded files and settings every X hours (every 8 hours for example) and CCleaner Professional will run silently to recover hard drive space and maintain your PC.
You can set exactly what CCleaner Professional will clean and when it will clean it.
For more information, see the product document - here!