Take a look at the discussions: you can find a link to a YouTube playlist with all the 24 episodes there, with English translations. Indeed, it is not important at all, just some fun little 30 second long shorts with some summaries of previous events and character presentations. The shorts all relate some bits of information about events and concepts of both Season 1 and Ren, such as the name of the circle (society), Yuuta and Shinka's past as the Dark Flame Master and Mori Summer, the Vanishment This World and Physical Linkage chants, etcetera. You won't miss out on absolutely anything new here. However, there arealso no real drawbacks. It's around 8 minutes total for the whole 24 episodes, and with the English translation in the discussions, you can comfortably sit down to reminisce about the cast's antics for a little while. if you're extremely into Chunibyo just like me, then I'm sure you'll enjoy 8 minutes of cute chibi dialogues between the main cast.

TL;DR: 8 minutes of extra cuteness, not necessary at all but also very easy to watch.