Because users have different operating systems, web browsers and computer hardware (including mobile devices and different screen sizes), online ads may appear to users differently from how the advertiser intended, or the ads may not display properly at all. A 2012 comScore study revealed that, on average, 31% of ads were not "in-view" when rendered, meaning they never had an opportunity to be seen. Rich media ads create even greater compatibility problems, as some developers may use competing (and exclusive) software to render the ads (see e.g. Comparison of HTML 5 and Flash).
A key benefit of using online channels for marketing a business or product is the ability to measure the impact of any given channel, as well as how visitors acquired through different channels interact with a website or landing page experience. Of the visitors that convert into paying customers, further analysis can be done to determine which channels are most effective at acquiring valuable customers.
It can be published as a book, and other people have already suggested what to include into ‘part 2’. As someone who has been asked by other people wanting to promote my products/serviced, I’d love to read about the merchant’s side of AM, e.g. various software that can be used, how to choose affiliate partners, what to include in the agreement, etc.
Professional gold affiliates take percentage programs and build a system around it, where they will create either advertising campaigns, a website specific to the offer, or a combination of the two. They then tweak the adverts and their side of the offer until they are making substantially more than their advertising or SEO costs – and then they scale.
My favorite style in this is article marketing. You create anchor content on your website or blog, then you build authority-content links to that content, effectively driving up the visibility. I've used this single strategy to rank hundreds of keywords in the #1 spot on Google, and I would highly recommend that if you're going to learn any marketing strategy, that you get really good at this one.