According to standard Kimbal methodology, Star schemas should really be used for everything, except when it is impossible to represent the data in a Star structure, such as when you have many-to-many relationships. Here you need a Factless Fact (or Bridge) table, made up only of Foreign Keys.
The other time you might need an almost Factless Fact table is to represent the current status of data in a Star schema, such as when you want to represent a current list of all products available. This would require a column ProductAvailable in your Fact table, so that it can be summed, and a foreign key relationship to the Product Dimension. You may as well stick this column into the Product Dimension and then import that table into SSAS as both a Fact and a Dimension.
The other time you might need an almost Factless Fact table is to represent the current status of data in a Star schema, such as when you want to represent a current list of all products available. This would require a column ProductAvailable in your Fact table, so that it can be summed, and a foreign key relationship to the Product Dimension. You may as well stick this column into the Product Dimension and then import that table into SSAS as both a Fact and a Dimension.
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