I have used joins and subqueries (in the where clause) in the past. But when I look at many of the exercises, there's a partially-written #SQL query that uses these features and CTEs and it is difficult to reason about the query and its pieces. Normally, that's when I'd write some exploratory queries to understand how to go from a set of tables to a specific result set (itself a table).

But the table rows seen in the preview may not be easily visible in the query results, which makes it more difficult to see whether one is on the right track.