DO NOT INSTALL THIS, EVER!
Apps like MacKeeper or any other maintenance apps like CleanMyMac 1 or 2, TuneUpMyMac or anything like these apps, installed on your Mac, while they appear to be helpful, can do too good a job of data "cleanup" causing the potential to do serious data corruption or data deletion and render a perfectly running OS completely dead and useless leaving you with a frozen, non-functional Mac.
Plus, these type of apps aren't really needed or necessary. They really aren't.
There are manual methods to clear off unnecessary data off of your Mac that are safer and you have complete control over your Mac and not just leave a piece of auto cleaning software in charge of clearing off data off of your Mac.
The potential of these types of apps causing OS X issues outweighs the implied good and benefits these types of hard drive or memory "cleaning" apps are written to do.
Plus, the software companies that write these apps make it hard to easily uninstall these apps if something DOES go wrong and these apps work in a way where you have no recovery or revert function to return your Mac back to its former, working state in the event something does go wrong.
These apps are, basically, useless and a way to scam new and novice Mac users out of their hard earned money for a piece of software that will cause more issues than it solves.
It is best to never, EVER download and install these types of apps.
The risk to your system and data is too great a risk!