Since a picture is worth 1000 words, pretty sure we're talking about this:



which I think is a Marriott thing when doing points bookings -- you can choose to use points on some nights and cash for the others.

And while I never used it, I believe what Keyser may be thinking of and is getting this confused with, is on the SPG side besides a straight cash rate and a straight points rate there was also a "cash & points" rate so (just making numbers up for an example) the cash rate might've been $200/night, the points rate 15k/night, or you could do C+P for $100-plus-5k-points per night, but whichever of the 3 you chose, it would apply to all the nights.

If this isn't what you were thinking, then I've just muddied the waters even more and apologize