I agree "episode description" isn't the best name for it, I tend to think of it as more of a "creator comment".
I use it to comment on the episode, share news, or ask questions, like cleo_san said.
I actually don't know how it appears on mobile, but I know that some people do read it since they sometimes respond to its content in the comments.
Well, not all of the readers seem to pay attention, but a great portion actually does =)
I, myself, love creator talk in the episode description, it sometimes contains additional info or just an update, of the creator is planning a hiatus, etc. 
In this regard it is quite useful!
The "creator's comment" - as @A_Toad just said (btw, hi there, we seem to be meeting often in threads, today! XD) - appears right below the last page of the episode and above the reader's comments (in the desktop version). On the mobile app it's only the pages and the creator comment, for the reader's reactions you have to click another button =)
And no, it does not appear as an episode summary, at least not on tapas... the first 1-2 lines of text are displayed when you share it on twitter though =) No clue about facebook tho ^^"
Thank you, @cleo_san , for taking the time to answer all my questions! As a newbie I'm still figuring things out around here. 
You're very welcome! =)
If you have any more questions, just ask, okay? Noone here in the forums will bite you for that, we're a pretty chill community =P Enjoy your time on tapas! <3
Yes, the episode description does appear at the bottom in the app also.
Here is how I use it. I use a lot of borrowed materials like Soundcloud music and Creative Commons images. Just last night, I launched a new series which uses text directly lifted from the projects of other Tapas writers(with their permission of course). I use this space to acknowledge the creators of those borrowed properties. I also sometimes crack an extra joke in that space which doesn't fit inside the normal text.
Originally, the episode description area was supposed to be searchable, like the series, only more specific. It doesn't work that way though. On some other threads I have seen it mentioned that that feature is broken, and has been broken from the start. Whatever it's original intention, most authors use it like an additional comments section, or ignore it.
The way I often see it used (and use it myself) is more as a kind of commentary from the author. A chance to comment on the page, leave a funny remark, pose a question to the readers, etc. Of course not everyone will pay attention to them, but I still like to use it for the aforementioned purposes.
I use the episode description not just to summarize the episode, but to also give information about what inspired certain parts of the episode, what to look forward to in future episodes, and sometimes I use it to give more details about a point that I don't think that I thoroughly explained. Examples of what inspired an episode sometimes come from certain scriptures in the Bible and events that have occurred in my life and in the lives of loved ones.
To me that sort of author comment space is kinda a place to be human. I've noticed that if you ask questions in this space, a lot of readers will respond to that, but I usually just make a lil jokey comment there, like if a character is lying very badly on the page then my note for that space might be a facetious "No one suspects a thing!" or "WOW XIRA, SMOOTH, VERY SMOOTH" -- just something small. I've found as a reader that when the author says nothing in this space, I tend to see the comic as very detached, and when the author comments in this space, it's easier for me to want to connect with them in some way!
I also would use that spot to share my link to TopWebComics, since I put a new vote incentive up with every update, to encourage folks to check that out.
I love writing episode descriptions. Usually, I write them on the first chapter on my work, and every remaining chapter would be a vague comment about what transpired in a later chapter. I gotta be careful though when sharing, because light spoilers MIGHT be alluded to in the descriptions. (Thanks Google+...)
I'm the kind of person who rambles a lot on my episode description. laugh, though I try not to make to much of it, I ended up writing how long words on it. ^^;
Letting the readers know of what you were thinking about the episode, the incoming episode, some news and announcement, the whole series itself, the promotion of your other project and stuff, or simply telling them how your days goes. It have a lot of use.
I use to think like it was a Netflix description of a single episode of a series: a resume. And i normally put two or three sentences to help pace the mood of the reader and some hints without spoiling my story.
I use it to leave a question, a experience I've having working on the chapter, etc, 
and yes on the app that space stills on the bottom
Incidentally, I've also discovered that the Episode Description is displayed as the excerpt/summary for when you link directly to that page here in the forums. Something to be aware of, since whatever is in there might look strange out of context.
Haha, all mine will look very strange then!
Since it appears right under the chapters, I use my Episode Descriptions for Author's Notes. I started posting writing on Mibba way back in '08 as a young teen, and made a habit of "chatting" with readers in the author's note section they provide at the end of each chapter. Now I can't imagine not saying at least "hi" at the end of every chapter no matter what platform I'm posting on.
So I just ramble at any readers who take the time to read it for a couple of paragraphs, or apologize for uploading a day late or something.
I think that's cool. People like authors who interact with them. On Wattpad, I'm constantly told how shocked they are that I reply to every comment I receive. And I'm like, "Why wouldn't an author do that?" Replying to every comment encourages readers to leave even more comments because they feel like they are being heard.
Hmm I use my episode description as a half joke comment on the chapter I've posted. However my comic is one of those random comedy slice of life comic things so there's not much else to say for me. Maybe when I do more story based comics I'll have more to say 
My personal rule is to keep all story content separate from interaction with readers. Thus, I use my episode description for a really short blurb about the episode (usually about a sentence long). If I can, I sneak some sort of pun or wordplay into it. If I want to talk to my readers, I'll post a comment on the episode so it's easy for them to reply to and interact with me.
