A ubiquitous example of this is the Facebook "Like" button, which the creator of which said she wanted to "solve the redundant problem":
> So how did the like button come about? What problem were you trying to solve?
I was trying to solve what we called the redundant problem. So for example, if you write "We're getting married!" all the comments used to say "Congratulations" over and over again. I found that really aesthetically ugly, plus, every time someone did say something heartfelt, the post was hard to find among all the other redundant ones. [0]
I find a similar situation on YouTube, where commenters don't add any insight or discussion to the video, they just say something like, "Great job!" or "Beautiful music!". Not a problem in itself, but when you have hundreds or thousands of these comments it leaves out real room for critique, questions, etc.
GitHub has a similar feature with reactions to issues.
However, one small concern I have is that such reactions might "dumb down" user/viewer participation and give the impression that using a reaction is all you need to do to have an opinion. Real discourse requires thought and reason, and not just slapping an emotional sticker on something.
[0] https://www.vice.com/en_ca/article/mbag3a/the-inventor-of-th...