The most obvious reason to build your email list is to maximize the value of your customers and your company revenue. However, it's also important to remember that your email list is a company asset. In the event that you want to sell your company, a high-quality email list can increase your company's overall valuation. Additionally, a high-performing email list can give your company additional revenue opportunities by giving you the chance to sell advertising space in your email products or send sponsored emails on behalf of partners or advertisers. You're not just building your marketing channel when you build email list. You're also building your company's total value. That's why it's worth your time to build a quality email list over time.
Some ad platforms will ask more of your landing pages than others, when running ads. For example, AdWords is much stricter, when compared to Facebook. AdWords typically requires that you do not have a ‘thin,’ site that is designed solely to collect leads. Because of this it might be a good idea to focus on using Facebook or Twitter, to begin with.