I'm missing a feature in Tableau Prep Builder: In the final output step when selecting "Publish as a data source" on Tableau Server, I have no option to classify the fields into dimensions or measures. Sure, in general Tableau does a pretty good job in doing that. Sometimes there are exceptions though that need human action. I would expect a similar way as if I would publish the data source via Tableau Desktop.
Related idea: Enable creation of user filter when publishing data source to Tableau Server (https://community.tableau.com/ideas/10306 )