input RLC filter of power supply

[Moataz Beheta]

Hi
In "Lesson 5: Schematic Design - Power Supply" video, it was mentioned that the input RLC filter should have a high cut-off frequency in Mhz.
why should it be in Mhz? why we don't set the cut-off frequency to, for example, 100kHz or smaller to prevent any noise like the filter of LDO regulator? I think that will make it more efficient to filter low and high frequency coming from USB port

another question:
before the inductor, there is another 1uF capacitor, why we added to RLC filter, and how did we calculate its value?

[ahernandez]

I've got another question: how do you calculate de 10nH value to let 500mA of current pass by the filter?

Thank you.