In general, the process to build and manage both models and reports in Power BI can be simplified to a few sequential steps that describe the “lifecycle” of this content. You can see this depicted below, as well as some examples of the various tools that you might use to support each of these steps. Shameless plug, Bravo, Vertipaq Analyzer, and Analyze in Excel were created by SQLBI, and SQLBI is involved in the development of DAX Studio, DAX Optimizer, and Tabular Editor.
Click through for an interesting table showing what fits where. If all you’re using is Power BI Desktop, there’s a whole world of additional functionality you’re missing out on.