ArcGIS Online: There may be cases where you would like to grant a User level role the ability to edit attributes but you would like to grant an Editor or Curator (or similar) role the ability to edit geometry of features.
From the layer properties you can set the editing permissions, but it applies to all users.
From the default viewer/map you can turn on/off editing, but that pertains to all editing types.
You can set user privileges so that they can "Add layer to new map with full editing control" even when geometry edits are not allowed, but this override is a one-time deal: You cannot save the map and retain the the editing rights.
Web AppBuilder does have this control within the Edit widget which is fantastic; however if you want to edit the same data on Collector for instance, those editing options are not available.
There are simply times when you would want different web maps using the same data to have different editing capabilities based on the user. I would suggest that these editing capabilities are set at either the map level (within the web map properties), or at the layer level within the web map itself, or even within the definitions of roles.