These are two core concepts that apply to art, to business, and to life. While we all like it when we have 'happy accidents', we can't count on them happening all the time.
As artists, our customers want to see some degree of consistancy in our work. How can we reproduce that color, that texture, that effect, if we don't know what we did in the first place, and how we did it? Consistancy can only come with the ability to accurately measure our materials and processes.
How do we really know what temperature our kiln is at? Is our kiln temperature consistant across the entire shelf, and from top to bottom? Does it have 'hot spots'? 'Cold spots'? How do you know?
Some materials allow us to 'eyeball' how much we use, while others are much more sensitive to accurate measurements. It's heartbreaking to loose a piece late in the process because of a mis-measured batch of material, or a un-calibrated kiln.