Some apps are distributed as Split APKs (multiple .apk files packaged together) to optimize resources. Standard Android installers cannot open them.
This app helps Smart Launcher to stay as the default launcher on devices that have the bad habit to reset the user choice.
Please note, you don't need to install this app if Smart Launcher is already working fine on your device. Also, you won't be able to use app shortcuts if you use this app to force Smart Launcher as default launcher.
If you have android >4.1 you probably don't need this app.
ginlemon.smartlauncher.bootfix on the APK Downloader homepage.