Cedar is (currently) based on Vega which in turn is based on d3. Obviously those layers of abstraction over d3 (Vega and Cedar) should make certain things easier.
In short, just about anything you can do in Vega, you can do in Cedar, however it is optimized for using the Cedar's "out of the box" chart types with feature service stats queries. So if you want to create a bar chart from a stats query, Cedar will make that much easier than if you tried to create the same chart just using d3. If you don't see the chart you want to make in the examples, then that's probably a sign that the effort it would take w/ Cedar would be closer to equivalent with it's underlying abstractions (vega or d3).
The one big "gotcha" with cedar Cedar is that it does not (currently) support very well (pretty much at all) multi-series charts (i.e. a timeline w/ multiple lines, or a mixed bar/line chart). We are working on a 1.0 release which will include that capability. That release will likely also either completely switch out the charting library to amCharts, or introduce the concept of a charting "engine" so that you can choose between amCharts, Vega, and maybe eventually others.