tldr: You need more money for measurements of economic growth to grow, whether you need it for actual growth is an open research question.
Take an acre of land for example. It is measured at 1 acre. Just because we decide to pretend that it is 2 acres is arbitrary and makes no difference in physical reality.
Though I would agree that money is far more abstract and obfuscated as measurement system and is at heart a confidence game. So, it may be that arbitrarily doubling the money supply could alter psychological perceptions positively or negatively even though it is pure abstraction. The word Voodoo comes to mind