Disk Cleanup is an older utility program that has been included with the operating system since the days of Windows 98. Until recently, the tool worked in Windows 10 much the same as it always did, scanning the drive and rounding up a list of all the unnecessary files and system detritus that you could delete with the click of a button. With a little extra work, Disk Cleanup could be set to run automatically, but some people chose to manually open and run the program when needed.
As Windows 10 has evolved, Microsoft has automated some of the housekeeping chores performed by Disk Cleanup and moved them into the system settings in a feature called Storage Sense. In the latest version of Windows 10, you can find Storage Sense by going to the Start menu, selecting Settings, choosing System and then, on the left side of the box, tapping or clicking on Storage. (Asking Cortana to open Settings or pressing the Windows and I keys on the keyboard to open the Settings box can save you some steps.)