It's the consumer version of "golden handcuffs." It creates a psychological bias toward vendor lock-in. Ican't use my PC Optimum points at a non-Loblaws grocer for example, which kind of makes it like Company Scrip or Canadian Tire money.

The privacy angle is it ties a purchase history database to an email account/identification number. You ever heard the story about the teenager whose parents found out she was pregnant because the store she shopped at sent her a "Congratulations" package?

Edit: IIRC, she wasn't even sure yet, but the store knew because it tied her purchases to her reward points and the analytics figured it out.