The WinSXS folder contains all Windows system components that ever met your system. All versions of all files, .DLLs in every version ever installed. When Windows installs updates, it drops the new thigs in the WinSXS folder and keeps the old ones there also. This means that every Windows Update you install increases the size of your WinSXS folder.
Windows 8.1 added new command line option for DISM.exe, /AnalyzeComponentStore. Running the command will analyze the WinSxS folder and tell you whether a Component Store Cleanup is needed or not.
In Windows 8, open Disk Cleanup Tool and use the Windows Update Cleanup option to clean the WinSxs. Microsoft released an Update that added the Windows Update Cleanup option to Disk Cleanup tool in Windows 7 also, so it's cleanable in 7 too.
As for the installer directory, Windows Installer UnUsed Files Cleanup Tool (WICleanup) is able to scan for orphaned MSI and MSP files in the \Windows\Installer folder and offers you an option to delete them. So use this tool, but fist uninstall what applications you don't need/use anymore.