Slices are a great way to improve query performance in a heavily partitioned SSAS Cube. The photo above shows where to add or change a Slice properties in partition properties dialog box.
If you ever get the following errors when processing cubes, it has to do with the Slicer property at the partition level. The first error message tells you it is a slicer, the next few messages will indicate which partition puked.
<Error ErrorCode="3240034361" Description="Errors in the OLAP storage engine: The restrictions imposed on partition slice where violated." Source="Microsoft SQL Server 2012 Analysis Services" HelpFile="" />
<Error ErrorCode="3240034318" Description="Errors in the OLAP storage engine: An error occurred while processing the 'FY2017Q3' partition of the 'InternetSales' measure group for the 'MyCube' cube from the AdventureWorks database." Source="Microsoft SQL Server 2012 Analysis Services" HelpFile="" />
Basically, SSAS will not assign a slicer to the partition unless the slice already exists in the Dimension. Since our time dimension is filtered to only valid sales dates, there will be no slices available for future dates.
The problem is that this means we need to add Slicer properties to the newly built partition each quarter.