KiwiNZ: Interest rates are a totally manufactured and mostly falsely manipulated means to control. Thats it, there is no real logic.
Only to a point. The rule of thumb is that a central bank is able to control the inflation rate, the exchange rate and interest rates - pick at most two. The other one, almost definitionally, winds up as the swing variable. Plus, while it's true that a central bank can intervene in the market to fix rates, if it tries to fix them at a level grossly incompatible with the settings needed to by an economy then the results won't be pretty - with a recession (eg as from Britain's exchange/interest rate policy in the 1920s), currency collapse (most of Latin America at some point in the last 20 years) and/or hyperinflation (Latin America again) usually resulting.
Muldoon's refusal to let interest rates rise to reflect economic fundamentals, admittedly alongside his poor fiscal management and crazy regulations, is a key reason we got to nearly 20% inflation and had a currency collapse in the 1980s.