You won't notice it with progressive render or gpu render, but if using cpu render quite often you will see everything apart from buckets with hair having finished. I've had a render with about 25 out of 28 cpu threads idlily waiting while the remaining 3 threads finished te hair, taking 2 or 3 times as long as the rest of the render. Which is why larger bucket size is not always best for cpu rendering. If I have a render of a single figure with transmapped hair I usually use a bucket size of 16 for cpu renders so as many threads as possible will be rendering the hair simultaneously.