Attention keeps dropping in any talk longer than 30 minutes. A section divider signals, visually, "take a breath here, a new topic starts now" — inverting the color scheme or filling the background is what separates it from a content slide.
The demo's ✕ still hangs a bullet list under the header "Part 2. Market Analysis," so it looks just like the content slide before it. The ✓ fills the background solid, leaving only a huge section number and a short title — unmistakably a new chapter.
Checklist: does color or layout alone tell you the chapter changed, does the text stay to a section number plus a short title, are dividers not so frequent that they lose their weight.
When to use
Use one at the start of each chapter when a talk is split into roughly three to five sections.