Getting someone on a mailing list at least provides the benefit of requiring them to think about you more and see your name more often. I know I have personally

Getting someone on a mailing list at least provides the benefit of requiring them to think about you more and see your name more often. I know I have personally bought things from vendors more because their newsletter (which I almost never actually read) would come and keep them in the forefront of my mind. On a few occasions, these newsletters actually have informed me of useful discounts, sales, or new products and caused me to buy right away, but mostly they just increase brand presence/mindshare. Even though it's not directly measurable, that's not a benefit to be discarded, IMO.