Rewards program possible?

[swguy]

... The idea of a rewards program is when customer's checkout with items they get reward points which can be redeemed on items on their next visit (making them more likely to come back).

This topic comes up periodically, and it always perplexes me.

I have never seen a study that supports the assertion that a loyalty program is a strong (say, top 5) motivator in a customer decision to do repeat business. And I have seen marketers argue that a loyalty program coupled with a bad customer experience increases the probability of negative word of mouth.

Is there hard evidence that loyalty programs are a critical driver in your space? It just seems like a huge administrative headache to me with very little payback.