Every time you put something into a measurement container, some small amount of the stuff stays in the container after you empty it out. The measuring scoop you use for flour, the measuring cup for cream, the mixing bowl to combine it.
We like to think that we can measure things for free, but it's just not true. Cooking a roast with a temperature probe in it makes it easy to hit exactly the right temperature, but the meat around the probe always cooks a little differently.
How big is the effect? A few percent, maybe. But it's not zero.
And almost always, the net outcome of the product is higher quality even if slightly lower quantity.
But it's worth remembering that every time you measure, it costs you a small amount of lost product. So measure wisely.