The only advantage to buying domains that you are not going to use - like Marcus does - is if you intend to sell those domains in the future like he does for a profit. The disadvantage is that every year you still have to renew those domains at on the average $15 a pop per domain. - Marcus has over 300 domains, that's $4,500 a year he is paying for all those domains. - Ouch!
When you buy a domain from a registrar, if you do nothing with that domain, then the registrar will create a "under construction" site for visitors to see. It doesn't hurt your search rankings as their is nothing on it anyway. Your real ranking comes after you put content on the site in which now the Robots crawlers have something to index. If you are going to use PPC for that site, then you don't really care about ranking.