Reusing styles is a huge valid reason. Even today Google Docs/Slides has a convenient “Make a copy” button that is easier for me compared to setting up a template.
I just copy -> rename -> open -> select all -> delete
For example, when (being dragged into) making PowerPoint presentations, I tend to manually style two or three slides (e.g. title page, chapter divider, content slide), and then create actual slides through "Right click -> Duplicate Slide".
I just copy -> rename -> open -> select all -> delete