For background on what Sharon is referring to, see here.

But there are two differences which are important. Certs have to be used within a fixed amount of time, or the certs expire, while points theoretically go on forever, as long as the account is still active.

So if someone is borderline on room nights for whether they will renew their status level or not for a given year, with certs, the member might have to just let them expire, or risk losing status. But with points, members have the choice to put off use until a year in which they are traveling more and not worried about making their room nights quota. Also, certs don't add to lifetime points, while Mega bonus points do, so it puts the certs award recipients at a disadvantage.