No of Aggregations Vs % of Performance gain

Hi,

For performance optimizing my cubes, I used the aggregation design wizard to create aggregations. The only thing that I am not able to understand is:

The number of aggregations and the percentage of performance gain (as shown in the design wizard) keep varying, when i change the AggregationUsage properties of the attributes of the dimensions in the cube.

Here is a set of rules for setting the AggregationUsage property, that I had read from a blog on the net:

1. Attributes that are not displayed = none
2. Attributes that are not used in any hierarchy = none
3. Extensively used attributes = Full
4. All other attributes = Unrestricted

I first set the Month attribute, Key attribute of the date dim as Full. (not sure if this is correct)

now,

if I set the AggregationUsage = default I get more number of aggregations (20-35), but the % performance gain is less (22%).

If I set the according to the above rules I get more performance gain (70%) but less aggregations (1-3)

My question is, which is the best one, and why

also please give some tips to set AggregationUsage property.

Regards