Where points become REALLY valuable is in situations where you are buying flights for other people, especially when they are people who have a tendency to change plans that the last minute. As others have pointed out, a points cancellation rolls right back into your account with no restrictions on who can use them, which isn't the case with refunded cash value.
Example of when using points is invaluable: say you would like to bring along a child's friend, and because you are a generous parent, you pay for the ticket. Kid screws up and gets grounded sometime before the trip, and parents regretfully call you and say that they are very sorry, but Susie will not be allowed to go after all. If you just cancel the reservation you are out the cash because no one but Susie can use those funds, but if you bought it on points you lose nothing. (This is also something to think about if you invite older folks such as grandparents, who may have health problems that could cause them to back out at the last minute.)
(And yes, I know that it's possible to re-use a child's ticket because TSA doesn't ask for ID on kids, but it's a bit risky, because TSO's have a sneaky habit of asking the child his or her name at security. If Annie is supposed to be Susie and forgets, you're going to be up the creek.)