Delta Update Question? URGENT

hi all BW Gurus,

If we already did delta update in source system level Like LO/LIS etc ,then why again we need delta update in ODS Object, if we want to load data into ODS Object.Or else If we don't use ODS Object and delta update from source system already happen then can we directly loaded data into InfoCube, If YES the why.If I am wrong Please correct me.I need complete details .Please reply me.Thank you.

regards,

VJ