I often need to draw on the map to exchange ideas with others. I can use the map notes in ArcGIS Enterprise map viewer or Draw widget in Web Appbuilder, but they don't support my smart pen very well.
As an alternative, I use snipping tool or MS surface pro whiteboard function, but this workaround has its limitations. for example, I have to work outside of my GIS work space and the map is not interactive....
Nowadays most mobile devices come with a touch screen, some with a smart/active pen (e.g. surface pro and iPad Pro), it make sense to have the built-in function to fully use these great input devices to write and draw on the web map, no matter what you call it: map notes, drawings, graphics, annotations...
Actually, I would like to see the pen support across all ArcGIS products. After all, we've been writing with pens for so many years before computer mouse were invented.
BTW, I tried the annotation function in ArcGIS Pro with an active pen, the experience is not good in the current version.