On the Audience Introduction Report, in Demographics Highlights, we are showing the composition for the highest indexing attribute value in a set list of attributes. For example, our "Holiday Shoppers" audience over-indexes on being aged 23-34 (for which the composition is 24%) with a Household Income of $75-100K (for which the composition is 17%).
Note that these are not the attribute values with the highest composition for that attribute, but the composition values for the attribute values with the highest index. For example, if we look at Holiday Shoppers on the Audience Comparison Report - we can see that the attribute values that have the highest composition for the Holiday Shoppers Audience for age group are ages 25-34, and $25-$50K for household income. But those are not the attribute values that over-index.
Looking at the Card View, and looking at age group and household income insights, we can see that, for Holiday Shoppers, the highest indexing values for age group and household income are 18-24-year-olds, and $75-100K.
Long story short, the Audience Introduction report helps save you time analyzing by showing you the attribute values that over-index, and then what their composition is.