It's important to take advantage of the window of opportunity when your company or brand is at the top of your prospects' minds. You can really get a pulse of what future engagement will look like by what people do when you email then within 24 hours of their subscribing to your newsletter, signing up for an offer, and so on. Plus, it's a great opportunity for branding and setting expectations.
That isn’t to say that sales-y promotions couldn’t ever create results—as marketing “gurus” have proved. The results just aren’t as good as they could be. Take the biggest gurus’ results—the ones they boast about—and calculate their conversion rates. Often their marketing is comparatively ineffective. They just have massive volume, so the sales numbers are impressive.