[asdff]

Think of it more as just getting to the one function that you are using. I think a cell free technique that people might have heard of even in high school biology at this point is the polymerase chain reaction. Rather than have some cell we grow in some growth media under certain conditions optimal for cell growth and harvest cloned DNA from these cells, we have isolated the involved protein directly (DNA Polymerase). We know exactly what temperature is most optimal for each step, and infact depending on what targets of DNA we are looking at certain temperatures may be more optimal for these targets. We know the exact pH that these molecules are most effective at and this might not even be a pH found in the cell but one determined empirically by measuring enzyme activity across a gradient of pH and/or temperature ranges among other potential conditions. We know the inputs and reaction and can supply just enough of these molecules as we need to drive satisfactory yield in order to decrease our costs. We can optimize the timing of this temperature-dependent reaction again to the specifics of the DNA molecule that we are amplifying. We can change how quickly this reaction is heated up or cooled down to optimize for product yield. We can change out components of this reaction such as our enzyme for ones that might operate faster with less accuracy, or ones that operate slower with higher fidelity, or ones found from other species that might have these properties, or engineered proteins that might have these properties.

Many reasons why you'd want to go cell free. You are no longer binned into the cell but are now just throwing things into a tube where you can control all the parameters that matter for your desired function.