First things first, what are you posting for? And what are you writing and replying for? If you are doing just to have fun then you can reply and post as any length you want. But if you use it to earn points so you could make money on it then you have to post for long, I asked you those questions because it is of no point posting or replying comments for long if you are not earning money from, or using it to catch fun.
When you are in a blog/forum/website your lengthy word post and comment is necessary, it earns you more points aside from that it proves that you are a good writer, you have to be cautious of word count when posting as it is of importance to you. There are blow/forums/websites who don't need lengthy replies and post just ho straight to the point, it depends on the platform also you know that you are being awarded points so your word counts should be much not brief, like I said it depends on the platform and you posting those lengthy replies or post increases your ratings because the Adkins who gave you this sites to post and reply on expects you to be exceptionally good with it that's why postloop gives you that trial first before letting you into these kinds of sites.