I just had a look at the BIEE Sample App V207 and noticed that the physical fact table 'F10 Billed Rev' is joined to 3 Time dimensions:
'D01 Time Day Grain'
'D02 Time Month Grain'
'D03 Time Quarter Grain'
What's the idea behind this - performance improvements when doing time series calculations?
Here it is maintaining three different levels so it can be helpful for aggregation tables and maintaining multiple LTS in BMM layer. The main purpose is for performance tuning, the server hits any of this tables based on the time level used in analysis.
For ex: If the analysis is based on month level then the server will hit Month level table.