Hi @Bud ,
That is a good question. In that presentation Jason Hine, shows a general picture of the platform and talks using Arcade to create content on the fly without changing your schema. That is true, but depending on where you apply this the scope of the functionality available will be different. Have a look at something called the profiles: Profiles | ArcGIS for Developers You will see that Arcade can be used in Attribute Rules, Field Calculates, Labeling, Popup, Visualization and a lot more.
You will also have to consider versions (have a look at the version matrix: Version Matrix | ArcGIS for Developers , and you will see that functionality will depend on the version of ArcGIS Pro | ArcGIS Enterprise server | ArcGIS Enterprise portal | ArcGIS JS API | ArcGIS Runtime). ArcGIS Online is not mentioned in the matrix since it always uses the latest version.
Some "profiles" offer a lot more functionality than others. Take for instance the pop-up where you can access other layers and tables. The Visualization and Labeling profiles will not offer this and the reason is performance. When you show a pop-up it will normally be a single pop-up at the time as opposed by visualizing thousands of features and labels in a map at the same time. That is why the complexity of an Arcade expression can be a lot higher in a pop-up and still be responsive.
If you can elaborate a little more on what you want to accomplish, I should be able to point you in the right direction and provide some examples.