PowerPoint makes sure you have consistently capitalized and punctuated your slide titles and body text throughout the presentation. It can also check for visual clarity: it makes sure you haven't used too many fonts (or made them too small), placed too many bullet items in a list, or used too many words in a title or bullet item.
When PowerPoint finds a style inconsistency, a yellow light bulb appears on the slide. Note that to use this feature, the Office Assistant must be turned on.