Identify missing join values
Recently some Column Quality and Column Distribution checks have been introduced into the Query Editor, which are great.
A useful addition would be identifying Foreign Key values for which there's no corresponding Primary Key. A simple and common example of this would be identifying Customers who appear in the Sales fact table who don't appear in the Customer dimension table.
The join created by the developer would identify the Foreign/Primary Key relationship, and perhaps any such orphaned Fact table records could be highlighted against the join itself.
Currently such occurrences of this will usually result in Sales values posted against blank Customers in reports. The Customer value from the Fact table would have to be brought into the report to identify the missing Dimension table records.