Steve Stedman takes a peek at tempdb:
A worktable in SQL Server is a temporary structure that the SQL Server Database Engine uses to process certain types of queries. These tables are not explicitly created by users but are generated by SQL Server internally to handle specific operations that cannot be managed directly within memory. Worktables are stored in the tempdb database and are crucial for facilitating complex query execution plans.
Read on for examples of when SQL Server will use worktables and some good ideas when you spot worktables in the wild. They’re not inherently bad, but there are some performance problems you could experience around them.