Why is it beneficial for different parts of a human cell to have specific functions?

How would you imagine all the parts doing the same task? Which part would then monitor the inflowing and out-flowing substances if all are processing photosynthesis for instance, in an example where all the parts of a cell carried out photosynthesis?

It is like an assembly line. Each membrane bound compartment has a specialzed function that they are good at. If each compartment did everything you might still get the same amount of finished product but it might not be as good.