Why do I need power management if I have a great power cord?

Isn't it kind of unnecessary to additionally add a power conditioner if I have an expensive audio file grade Power cord connected to a component?

So you buy a Power conditioner from a hi-fi store and they say oh, you need a really good power cord to go with that and then another one to go from conditioner to the component. Do you need it all and why? Seems the last couple of feet before the component should be more than enough.