As it was nicely posted by Alex Mahrou (The ArcGIS Identity Crisis) it is very difficult to develop projects using ArcGIS Online content sharing capabilities. For instance, if a company wants to share maps with its clients only for them to view related content, it has to add these clients to the same organization or convince these clients to buy ArcGIS Online Organizational accounts by themselves. This raises costs enormously. There should be a way to share maps (apps and etc.) with private clients that do not have ArcGIS account. Sharing with public is not always the right solution.
Moderator's Note: This Idea has been marked as a duplicate of reduced pricing for viewer only accounts please consider voting for this functionality on that Idea.