It really varies. I'd also preach the importance of quality over quantity, but sometimes that depends on the context, and what the particular subject is. Especially with forums, plenty of discussion topics really don't need an in depth response. At the same time, sometimes a lengthy post is a great way to show everyone that this particular subject is very important to you. Or sometimes it's just someone throwing a lot of fluff into a post, as if they are writing an essay with a minimum word count requirement.