Looking only at only a variables Volume or only at it's Percentage can be misleading and often it's important to look at both and the relationship between them. We find it useful combining these views into one graph instead of having to manually eyeball two graphs and call peoples attention to points in each.
Suggestion is to allow us to graph both Volumes & Percentages on the same Trend view. A sample of this is below with Volumes as bars and Percentages as Trends: