What I know placeholder is used so bots don't automatically post new chapters from other site
To avoid the bot of automatically upload trash machine translated chapters, cuz they give more notifications and they mess up the chapter list
I think it's to stop bots or beginners from uploading bad translation? Cuz usually (when there's no official translation) it takes around 3 days for someone to upload the chapter, maybe more. But sometimes you can find mangas/manhwas with like 3 versions of the same chapter each with varying qualities. So the main uploader just puts a placeholder to stop that from happening.
What is the function of uploading placeholder chapters? It is so common, but I don't understand what use it serves?
Does anyone know?