Hey! How soon is this research project due? I want to give you something comprehensive 'cause lots of data is great, especially for anecdotal stuff. I can probably give you 1000 words if I sit down and think about it on my commute to school tomorrow. And just to clarify, I can speak about anything regarding fandoms and fanfiction communities ? It doesn't necessarily have to pertain to kpop?

EDIT: and would you be able to tell me the research purpose / results after you finish analyzing/coding the data you collect ? :')

Since the only thing I know is Kpop, I'm just going to talk strictly about that as a prime example, if you don't mind.
One positive aspect of joining a Kpop community is networking.
You may find a sense of security knowing that there are other people who are passionate about the same interests as you are, especially if you're introverted in real life and don't feel comfortable enough to share a part of yourself without feeling like you're being judged for it. I am such a case myself. It was only last year, when I first logged in after a long time, that I felt comfortable enough to start making friends through putting myself out there through graphics designing.
Another positive aspect of being a part of a Kpop community is its diversity. You meet all sorts of people of different backgrounds, ethnicity, gender, etc, with their own perspectives on Kpop. You can have discussions on all sorts of things regarding Kpop or just Korean music in genre, or anywhere past that. For example, the rather questionable trends of cultural appropriation that can be seen not just in K-pop but in Korean society as a whole, or just any society in general (i.e blackface, dreadlocks, stereotypes, you get it) as well as other social issues (misogyny for example). When people talk about these things, it is educational because while K-pop is fun and poppy, you also need to be aware of its superficiality too, if this makes any sense.
On the other hand, these points can be used to prove the opposing argument.
For the first point, it's also quite easy to join in the bandwagon of increasing negativity. I don't think I need to go more in depth with this, since it's pretty obvious why it would be detrimental, but to summarize.
Fan-wars.
Sasaengs.
Predatory behaviors online.
Cyber-bullying.
istic fantasies :/
You'd lose faith in humanity if you already haven't done so :^)
I hope this helps a bit :)

Well, in my case, I got a new family through kpop
I found people whom I could talk to, about things my friends here never understood.
When people around me mocked me, I had people who'd support me, be it making covers or writing fanfiction
So basically I was able to find another support system

Even now, I'm closer to my 'internet friends' than a lot of people I see everyday