A clean up is both hardware and software. For the hardware side, we can remove the dust that clogs your fans because it can damage the motors of the fans and break them. On the software side, we can remove viruses (malware, spyware, etc.), annoying pop-up windows, temporary files, program installation residues, and so on. It is important to do this from time to time to make your computer lighter and to avoid some of the problems that can be costly to repair.