Apple is generally known for creating a stable operating system that requires few extra bells and whistles to function and maintain a secure operating user environment. While there are hundreds of utilities and security applications promising better functionality, often times customers come up with the regret of reduced performance. While SOME offer true benefits, more often than not the cons outweigh the pros.
MacKeeper, TuneUpMyMac, and other related utilities offer to get your computer running at optimum levels, but only if you pay for their product. All you end up getting is a program that slows down you computer at start up and is limited in what it truly offers. Norton/Symantec AV can be beneficial in protecting your computer if you are illegally downloading content or accessing questionable sites but it also comes at a cost to overall performance.
The best solution is to run the Apple updates when available and limit the extra utilities that do not come with the computer. Apple has done a reasonable job of keeping abreast of any security issues and providing an update to patch or correct the issue.
One final tip is to ALWAYS know what you are installing before you approve and install it.