Query Performance Tuning - Expert Cube Development with SSAS Multidimensional Models - page 217

Some queries would not benefit from aggregations, some would be slightly
faster, and some would be a lot faster; some aggregations would be more
often used than others. So if you set this property to 100% the wizard would
build all the aggregations that it could, and you'd get 100% of the performance
gain possible from building aggregations. Setting this property to 30%, the
default and recommended value, will build the aggregations that give you
30% of this possible performance gain - not 30% of the possible aggregations,
usually a much smaller number. As you can see from the following screenshot,
the graph drawn on this step plots the size of the aggregations built versus
overall performance gain, and the shape of the curve shows that a few, smaller
aggregations usually provide the majority of the performance gain.

• I Click Stop : This means carry on building aggregations until you click on

the Stop button. Designing aggregations can take a very long time, especially
on more complex cubes because there may literally be millions or billions of
possible aggregations that could be built. In fact, it's not unheard of for the
aggregation design wizard to run for several days before it's stopped!

• Do Not Design Aggregations : This allows you to skip designing aggregations.