Registration swatch merely means that it's used for printer marks and appears on all ink plates. Nothing beyond that is implicit. Not the color, nor any otehr specifics.
Registration is 100% of all used colours (CMYK and/or Spot).
It should never be used as a rich black (as one contributor to this forum maintained several moons back). NEVER. EVER.
If you are drawing your own trim, fold or crop marks, use Registration.
That way they will show up on all plates.
As long as you are not using spot colours you may possibly use Registration for the black in opacity masks but it’s really more professional to make a 100% CMYK swatch for that.
Thanks for the response guys.
So from what I understand if I want a an object to appear "white" I should be filling it with a "white" swatch, compared to just leaving it filled with the "registration" swatch.
Unless you happen to be using a spot white, in which case spot white will be included in Registration.