Why does the feds always have a "money supply" management strategy. What are the implications if we don't?

I don't see why the money supply is something the feds need to control. Why don't they just let it float and not do anything about it. Why are there these episodes where they have to do a "monetary contraction", "monetary expansion", etc. What are the implications of not a "money supply management" strategy?<br><br>&#x200B;