I’m a big fan of self-documented semantic models. Business users have a hard time getting their way around complex models and descriptions can go a long explaining the purpose of metadata. After waiting for years for Excel to support field descriptions (the wait is still on), the December update of Power BI Desktop now supports them.
The new Field Properties window lets you enter descriptions for self-service data models. When connecting to Analysis Services, descriptions just light up on hover. A true Christmas gift! And Q&A in Power BI Desktop makes it ever better.