When you delete files, they are stored in the Recycle Bin until you empty it and actually free up space for new files to be created. This means that it’s good to empty the Recycle Bin regularly to keep your hard drives tidy. The tricky thing about this is that there are a bunch of files that you may not be aware of that should be placed in the trash and aren’t. These files are dubbed "temporary files."
Whenever you visit a website or install a new program, temporary files are created in specific directories on your computer. These files serve an important purpose at the time, but once you are done viewing the website or installing the program, they no longer need to exist, but they aren’t necessarily automatically deleted for you. That is why it is important to run the Disk Cleanup utility around once a month to go looking for the temporary files that are taking up precious space needlessly. Those files can and should be deleted so as not to give the false impression that you less have free space than you actually do once the temporary files are removed. Just like in our homes, it is important to take out the trash regularly and to go searching for junk we no longer need to make space for new things we do need.