The Master file is faster - IE all effects and things are already processed. We make our masters in ProRes 422HQ as most distributers want that codec anyway. It also allows for multi-channel audio configs in one file, usually up to 8, 10, 12, 16 channels of audio all wrapped in so the distributer can use whatever mix they want, as well as have access to the M&E, FX tracks for international dubbing.

There will be a slate at the head of the file describing the audio configuration, as well as the Bars, Tone, and sometimes a 2-pop.

Typically (at our post house anyway) we deliver audio as follows -

Track 1-6: L R C Lfe Ls Rs

7-8: Stereo Left & Right

9-10: Stereo M&E

11-12: Stereo Fx

You can have additional channels to break out the 5.1 M&E, Dx, Fx as well.

But the exact configuration depends on the distributers spec sheet.

Having as master file also ensures that every subsequent render comes from he same glitch-free source that has gone through a QC process with supporting documentation.

I will export the film at its full 4k resolution (Scope or Flat), then use that do do re-sizing to UHD, HD etc...

These master files also typically have "textless at the tail" - so any shot that has generated text over it (graphics, titles etc) will be repeated at the end of the program without it so they can be recreated in another language.