If Chuunibyou demo Koi ga Shitai! is the sandwich then Chuunibyou demo Koi ga Shitai! Lite is the side order of fries that goes with it making it more enjoyable.
Chuunibyou demo Koi ga Shitai! Lite is nothing more than 5 or 6 minutes of pure comedy which basically shows the relationship of all the main characters. There really isn't much more to it than that.
If you enjoy Chuunibyou demo Koi ga Shitai! and have a few minutes extra to spare and want a good laugh then you will get it with Chuunibyou demo Koi ga Shitai! Lite.