Are cables additive or subtractive?

There’s lots of debates here about the effectiveness of cables. Let’s please keep that elsewhere so we can have a DIFFERENT discussion about cables.

Let’s assume for argument’s sake that yes, cables make a difference and that it’s worth paying for that difference.

Lets assume that is true, then lets ask the question:

• Do cables ADD or SUBTRACT from the signal?

Again, for this thread, assume cables change something audible.

What do you think and what are your experiences?

Also, let's try to avoid sweeping generalities and try to focus on what happens along this axis:  Subtraction or addition.