The basic idea is to avoid having high cardinality columns in an SSAS tabular model database. The reasons are. 1. It takes a long time to.
SQL Server Analysis Services (SSAS) Tabular is a popular choice as it can be much more or less depending on the cardinality of your data).
The slow MDX happens when there is a high cardinality column in the rows and selection is done on joined tables. DAX performs well; MDX SSAS Tabular Model - DB compression is not optimized. - MSDN.