I never thought much on length of a post. I like to write and post according to the requirement of writing sites where I write. As I confessed many times I am not a professionally trained writer. I like to share about incidences,experiences, people, behavior, society and much more that is happening around me in day to day life. I started online writing through blogspot blog with posts ranging from 200 to 1000 words. Later I found Bubblews and start writing short posts there. I enjoy both kind of writing either it is long post or short post writing.
Although I read many articles that supports long post writing ranging from 200 to 2500 words. Behind this they give reason that Google searches works on post length basis i.e. top most search results for most of the keywords ranges between 2000 to 2500 words. and longest articles receive more external traffic rather shorter articles. Reference: https://goo.gl/0k53D
But it is not unanimous thought. Some advocate “short is sweet”. They believe that unnecessarily elongating any article could lessen the impact or effectiveness. For reference use Seth Godin’s blog where you will find most of the posts are short in length but they are shared hundred, some posts shared thousands of times.
As I understand you can’t say long post is better than short in terms of getting good traffic or in terms of earnings. It all depends on writer, writing style and content. If article could narrates things in short post there is no need to put filler words just to increase the length of the post. Other factor that affect the length of the post is writing style of the writer. Some writers like to write thing to the point, others like to involve their readers by doing conversation with them. Obviously article wrote in conversational or interacting mode will be more lengthy.
Do not bother about length of post. Just follow the rules of site where you write and enjoy your writing.