What is the Mul's Tireless ability used for?

Question

Tireless: You need to sleep 6 hours in a 72-hour period (instead of a 24-hour period) to gain the benefit of an extended rest.

Is this ability just flavor in that it allows the Mul to go without sleep for 2 days, or does it allow the Mul to gain the benefits of an Extended Rest with less sleep on a daily basis?

In those 72 hours most parties will take 3 extended rests. Can the Mul stand watch for 2 of them and still gain the benefits of an extended rest? Or perhaps 2 hours/day of sleep is sufficient?

Answer 1

It's mainly for flavor. Mechanically, you only need to do an extended rest every three days, and, yes, that's perfect if you want a Mul to stand watch for the rest of the party. There's no daily benefit, and breaking up the rest across multiple days isn't useful for Tireless.