Not everyone thinks the same all the time. The video you make by thinking about something can sometimes mean different things to different people. To avoid this, it is important to add descriptions to your posts.
In addition, if you are speaking in your videos and stories, if you add the description or subtitle feature, you will create an area where people who are hard of hearing can reach you and can access to your content.
Finally, in some cases, people may not be able to listen to the videos with the volume up, or they may not even have time to watch the video. It is also very important to write a short description for this.