Mine is based purely on absolute cost - I earned a lot of my points through business travel.
So, for leisure, if I want to stay in an expensive luxury hotel, then as long as I'm not getting ridiculously low value, I'll generally redeem. E.g., just booked Ritz Carlton Okinawa, and am getting approx. 0.5c / point of value. But the cash rate is high, so would prefer to save money for other things.