Federal structure: positives and negetives

Hi,
This post , I am writing about federal structure in Govt administration in India. As the constitution guarentees federalism ,but it also puts a condition .."union of states".
The defination of federalism, thus varies from country to country , as it's different in US which also provides freedom for secession of states.
              Wer have to focus on both the  aspects ,concerned with federlism. In India, it was designed to keep the powers of states intact , with centre given residuary powers . It is well understood from this that the makers of constitution pushed for both the aspects. They wanted neither centre to subdue the powers of states nor states to behave as dictators in policy making. A clause was also inserted in constitution that while the time of shaping anynew law, which damages or subdue or interfere in the powers of state,center must act on the basis of opinions ,provided by states or state concerned.