|My cat reading a book.|
The optimal response to someone is always the one that conveys a maximum amount of meaning and minimal amount of fluff, while still keeping your response neat and understandable. This is one of those guidelines that seem intuitively obvious in discourse but is easy to violate.
When responding to someone it is often the case that you want to be as verbose as possible to make sure that the message is transferred reliably, but the truth is that the only misunderstandings we can preempt are the kind we ourselves can conceive of.
Other people might have completely strange misunderstandings alien to our way of thinking. Therefore a long comment can actually explain something that the other person already understands in detail, and miss the fundamental part of your communication they don't quite get.
When someone has to read a large amount of text, a higher cognitive load is imposed on them. They are more likely to miss things and lose attention, if only briefly. If you are writing something, no matter how well written, if it is too long people will have trouble keeping it in their heads. That means that they would have to reread parts before they respond, or quite commonly you will find that they just respond to what they remembered in the first place, which could already be distorted by the time they finish reading or listening to a long comment.
When you write long pieces of text, someone may not have time to adequately respond, giving responses that don't address things you originally said. Alternatively, they can give a very long response in which you are now faced with the same prospect of reading a very long piece of text. You may meet a misunderstanding in this long text which renders the rest of it neutered. For example if an animal rights activist is trying to stop fishing, and finds out you are a fisherman, they may assume you use hooks and kill fish, when it could be that you use nets and release fish back into the water. A long comment on the evil of hooks would clearly be a waste of time when addressing you. To avoid this happening, shorter text is almost always better.
If your desire is to truly communicate something, you should keep in mind that you don't possess a right to your audience, you have the privilege of their attention. It makes sense not to abuse that privilege. Sometimes it is hard to keep things short, but with practice it is very possible to at least make things more brief.
I noticed a massive improvement in the productivity of discussions I had when I reduced the length of my writing. It seemed counter intuitive at first, and removing certain things I was itching to say was hard, but it paid off big time. I referred mostly to writing here, but the same concept can apply equally well to discussions in person. Our aim should be to communicate understanding, not to drown people in words.