Precision dice are carefully weighted on every side and manufactured under stricter conditions than your average dice. They are not perfect- no dice are- but they must be within 1/ 10,000 of inch dimensions for the most precise measurements possible. The purpose: make the dice as balanced as possible, with next to no bias for landing on any number. It’s a painstaking process to make precision dice, and it must be done using cellulose acetate. Certainly, anyone worried about any bias in their dice might seek a set of precision dice. However, it’s challenging to find a set of precision dice for D&D. Make sure the company is reputable too- and it’s truly precision dice.