Question: What is the Data Guard angle on this question if any? If there is none I would consider closing this and reposting in the "General Database" forum.
To know the answer, you have to understand what grain is. You can find detail on there here: Chris Adamson’s Blog: Rule 1: State Your Grain
Slowly changing grain is one where the fact table does not change much. Typically in a DW environment, this would be a fact table that is there to support other facts in the warehouse.
As mseberg said, this is a Data Guard forum, not a DW forum. Choosing the proper space can make all the difference sometimes.