Hi,
One of the most important design decisions you have to make when building PBIX or SSAS 2016 Tabular models is whether you import/load the data from the source system into memory or if you use Direct Query mode and let the source system process the report queries. If your source system is a supported Direct Query data source, and the model you're building is more than a quick pilot/POC, then you have to know and evaluate the many trade-offs such as performance, data freshness, modeling features supported, maintenance, etc.
I tried to summarize many of these factors and considerations in a Word document available for download from my blog:
SSAS 2016 Tabular: In-Memory vs Direct Query
Note: This document should not be viewed as comprehensive and per my blog more testing and research on the DAX restrictions/limitations and the SQL query plans generated across source systems is needed.
-Brett
