What's a likely change you'd make on one of the masters, as opposed to changing a slide directly?
A change to font style is a good candidate. Imagine that you wanted the first level of body text to be smaller on all your slides, so you could fit in more top-level bullet points.
Instead of changing the font size for that level of text on every slide, go to the slide master and change the font size for the top level of text. The change is applied to all the top level text on your slides — including existing slides and new ones. You'll do this in the practice session.
Other types of text changes you'd make on the master:
- Font type (such as Arial, Tahoma, or Verdana).
- Font styling (such as bold, italic, shadowed, or embossed).
- Paragraph settings (such as text position, spacing between lines, or margins).