This plugin will enable Smart Launcher to use some extra features. Actually you need this plugin to turn off the screen with a double tap using Smart Launcher. The plugin is very lightweight (only few kb) and doesn't influence battery life and memory usage.
PLEASE NOTE: SL extra requires some advanced permission (just to turn off the screen indeed). So after enabling it, you won't be able to uninstall this app unless you disable it in the SL's preferences. Then you will be able to uninstall this app like every other app. Here is a video tutorial: https://www.youtube.com/watch?v=lV7cjqdWXro
If you think this procedure is too hard for you, just don't install this app. You will still be able to use the most part of the Smart Launcher features.