The minimum
A minimum faan rule says a hand must reach a certain value to be allowed to win. With a three-faan minimum, a cheap hand of four chows is not enough by itself; players must build towards dragon pungs, half flushes, all pungs or other scoring elements. That makes the game more interesting but slower.
Home games often play with a lower minimum to keep hands flowing, especially with beginners.
The limit
The limit (or "max") sets the most any hand can be worth. Limits keep a single lucky hand from deciding an entire evening and make stakes predictable. Common limits are eight, ten or thirteen faan.
Strategy under a minimum
With a minimum, players must plan for value from the start: keeping honour pairs, steering towards one suit, or holding concealed hands. Discards also become easier to read, because opponents' hands must contain scoring elements.
Agree before you start
Both numbers — along with the faan list and payment scale — should be agreed before the first hand. They transform the game more than any other rule.