[Avodah] S"A Principles

[Richard Wolberg]

Reb Joel asks:
does anyone know of a theory as to why the Mechaber in some cases quotes Talmudic sources (or Torah or Rishonim) and in others just states the halacha? 

My theory is that when it is either a well known halacha and no reason to question it or at least, when the Mechaber thought it to be indisputable, then 
it was felt there was no reason to quote sources. OTOH, if was felt that there would be many questioning it, then the sources quoted would obviate 
that from occurring.