The Preheader references the area before the main content. It's an excellent opportunity to grab a bit of extra pre-content web real estate. It's got a degree of prominence in the inbox, so it would be a waste not to use it for promotional purposes. Try popping a couple of links in here. Some companies find that they get the most clicks on links within their preheader
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.
Bloggers are the most obvious example of focusing on this email marketing strategy almost exclusively. SaaS (Software as a Service) businesses are another group that typically heavily emphasize content emails. Of course, bloggers, SaaS businesses, and everyone else can send content emails while also using the other email marketing strategies. And you should do it, too.