When should i use Cubes

Could some one explain to be when we should go for cubes. I am confronted by this question everytime i see a non detail report and I am not sure if i shoudl use a cube

You should consider building cubes once you have your model defined and populated. They can be leveraged for reporting and ad-hoc analysis immediately. If you are using SQL Server, they are very easy to build if you follow a star schema with conformed dimensions. The real challenge is building the hierarchies in your dimensions and setting the correct partitions and aggregation level so they perform.