Benefit is a more loosely coupling between dimension and fact table .

It mays save up from need of recalculating the fact table if something go wrong, because the fact table contains only the reference to the entity contained in the dimension instead of the reference to the entity at a specific time .

Very often Sql Server is IO bound, so for the DBMS to perform a join on 2 columns instead of one is not problem since there is plenty of CPU