These really depend on the product. Kwoosh, the product in the article, is a team based project management tool and so requires a way to add other team members.
As for transactional emails, we have found that its the planning, writing, designing, producing content for them that takes time and not the actual sending process.
Having read Josh's eBook on mastering email it's good to see him sharing more of his knowledge in a free course...look forward to following along with the course.
Like a few other people in the comments here I started a 12 things in 12 months, where I will complete one different project each month.
January's project was http://finishonethingtoday.com, it managed to hit the top of HN for a few hours and got a lot of attention and continues to bring in visitors and has opened up a few new areas for potential projects in the future :)
It's a case of making it easier to get the customers permission to market to them in the future. More people will "like" your page on Facebook with a single click, than visit your website and fill in a form.