The main fact behind creating universes is "Business users
need not have strong SQL back ground. But sometimes they
need to develop reports". In such case the importance of
universe comes. The universe designer needs to have a strong
SQL back ground and he/she will create universe which in
turn has objects like dimensions, measures, etc,... 

The business user then uses these objects just by dragging
and dropping in the query editor pane. Dragging, dropping
and running is more easy for him rather than writing SQLs by
his own.

I totally agree with the answer given by Jansi. Creating 
universe is simplyfy the business users just to drag and 
drop the objects they want to create the report.