Though PPC is today the most popular advertising method, used by a majority of the websites for monetization, there are some major disadvantages.  Unless you closely monitor your websites, you do not know who is advertising on your website.  Also many ad networks use geotargetting, so you will never see the advertisements displayed in other countries.

For other advertisement methods like banner advertising or paid reviews, the advertisements are constant, so you know which products are profitable and sell well online.