You don't need "cleaner" or "maintenance" apps to keep your Mac running well, and some of these apps can do more harm than good. Most only remove files/folders or unused languages or architectures, which does nothing more than free up some drive space, with the risk of deleting something important in the process.
These apps will not make your Mac run faster or more efficiently, since having stuff stored on a drive does not impact performance, unless you're running out of drive space. In fact, deleting some caches can hurt performance, rather than help it, since more system resources are used and performance suffers while each cache is being rebuilt.
Many of these tasks should only be done selectively to troubleshoot specific problems, not en masse as routine maintenance. OS X does a good job of taking care of itself, without the need for 3rd party software. Among other things, it has its own maintenance scripts that run silently in the background on a daily, weekly and monthly basis, without user intervention.
Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released over 12 years ago. The only malware in the wild that can affect Mac OS X is a handful of trojans, which can be easily avoided by practicing safe computing (see below). 3rd party antivirus apps are not necessary to keep a Mac malware-free, as long as a user practices safe computing, as described in the following link.
Read the
What security steps should I take? section of the
Mac Virus/Malware FAQ for tips on practicing safe computing.
