Before you get started with SAP HANA…you should also consider cleaning-up your backend system first
90% of analyzed customer systems show significant potential to improve the data quality and accuracy of transactional data. If your SAP system belongs to the 90% case then you should think about cleaning it up – in general but also as preparation for utilizing SAP HANA. Otherwise you will get the planning or reporting data faster, but the data won’t have a better quality and you do not make better decisions.
Read the source article at SAP Network Blog