Its depends on your project requirement. Customized cubes are not mandatory for all the projects. If your business requirement is differs from given scenario (BI content cubes) then only we will opt for customized cubes. Normally your BW customization or creation of new INFO providers all are depending on your source system. If your source system other that R3 then you should GO with customization of your all objects. If your source system is R3 and your users are USING only R3 standard business scenarios like SD, MM or FI... etc., then you don’t want to create any info providers or you don’t want to ENHANCE anything in the existing BW Business Content. But 99% this is not possible. Because surely they should have included their new business scenario or new enhancements. 

Its depends on your project requirement. Customized cubes are not mandatory for all the projects. If your business requirement is differs from given scenario (BI content cubes) then only we will opt for customized cubes. Normally your BW customization or creation of new info providers all are depending on your source system. If your source system other that R3 then you should go with customization of your all objects. If your source system is R3 and your users are using only R3 standard business scenarios like SD, MM or FI... etc., then you don’t want to create any info providers or you don’t want to enhance anything in the existing BW Business Content. But 99% this is not possible. Because surely they should have included their new business scenario or new enhancements.