I pretty much live in Advanced and in my games, I pretty much have a 2 paragraph minimum standard, but posts oftentimes turn out being way more than that. 

I like to give people the option to reply even if they don't have that much to contribute to a particular scene/ they're hitting a writing block that completely screws you over. It rarely happens that people post the bare minimum, but I like to leave that option there because sometimes there just isn't 3+ paragraphs worth of things to contribute, and needless padding is kind of awful, especially if you're just regurgitating the exact same stuff that was covered in another post.