Are savings necessary for economic growth?
I don't know if you're arguing a theoretical framework or whether saving is important for real economic growth. In theory a special case where all consumers would spend 100 % (MPC=1) of their income is possible to argue - the framework would be loaded with questions - it might, for example, make banks redundant.

In basic economic models savings is often considered equal to investment (you see a variation of S=I in many macroeconomic models) which means that all saved income is used for investment and therefore expected to expand the economy for future periods. In real life the relationship isn't quite this straightforward, but the basic idea still holds.