I remember a throwing class at Alfred University, one of the first ones with Val Cushing. He asked us "how much should a mug weigh ?"
Numbers were thrown around, till my friend Matt Towers said - "however much it looks like it weighs". Bingo !
That's the exact match point in the eye-hand relationship.
When we approach a mug, or any other functional pot, our eye (brain) sends our hand a message about what to expect as to the weight and feel to anticipate when lifting it (if full or empty). That's what makes a "good" pot, good in the sense of creating that match between the look and the feel.
A mug , of course, has more aspects to it - a handle we can trust and a rim that is nice to put our lips to. In addition are the personal-subjective prefferences we all have and those are what make the mug such an intimate, functional pot.
I'm a potter who's in love with clay. If I'm away from my studio, I miss it. I truly think clay is the best material ...