One big advantage of building Sales Funnels, is that you will collect potential client contact and email information. So, you are taking traffic from a good portion of paid advertising and building your own organic marketing channel which can be reused over and over via email marketing. This gives your ppc campaigns much more bang for the buck!
Sales Funnels can come in different forms and be as simple as a few pages, mostly with visuals, to ones which span 20+ pages or have videos anywhere from a minute long, to some that are over an hour long, and are then followed up with more emails or levels of commitment.
It all depends on the product or service. Generally speaking, the larger the financial commitment you are seeking from your client, the more intricate, lengthy, elaborate and spread out your Sales Funnel will become.