We have different use cases for subtitles. But they are primarily for making sure your audience can follow what's going on in the video. It could be helpful for TV news, as customers are sitting in a restaurant, or it could be helpful on your social media - where most people will watch your videos with the volume off -... Or if you want to make sure that deaf people can follow the video as well.
There are some rules for subtitles we will not list here as there are plenty of sources like this one here.
The golden rule is that any subtitles are better than none. A transcript can cover a lot in this for you so if you cannot invest more love and time to transform your transcript into subtitles, alugha will use your transcript and export it as subtitles for your audience.