To develop an effective plan for SEM requires an understanding of the relative strengths and weaknesses of SEO and PPC marketing.

Advantages of SEO

Few would argue that SEO is potentially the most important search marketing approach for marketers since most searchers click on the natural listings.

Indeed, research shows that some searchers NEVER click on the sponsored listings. Others still don't realise these links are paid-for.

Generally, the 80:20 rule holds true with 80% of the clicks on natural listings and 20%[1] of the clicks on the paid listings as suggested by the first Stats box earlier in this section.

A key benefit of SEO is that it is relatively cost-effective since there is no payment to the search engines for being placed there. Many companies bid on these phrases through paid-search, so giving opportunities for those who use an SEO strategy for the tail.

 Additionally, the cost of SEO is relatively fixed, independent of click volume. Effectively, the cost per click from SEO declines through time after initial optimization costs and lower ongoing optimization costs. Conversely, paid-search is essentially a variable cost.

So, there are no media costs, but resources are necessary for key phrase analysis and to complete optimization on the website pages.

 Together with paid-search it can also offer a highly targeted audience � visitors referred by SEO will only visit your site only if they are looking for specific information on your products or related content.

 Disadvantages of SEO

The challenge of SEO is that there are over 8 billion pages[2] in the search engine indexes with your position in the SERPs dependent on a constantly changing algorithm which is not published. So making your pages visible may require specialist knowledge, constant monitoring and the ability to respond.

As a consequence, the biggest disadvantage of SEO is a lack of control. You are subject to changes in the algorithm.

There are other possible issues. You may be prevented from competing on a level playing field, because competitors and even affiliates may use less ethical black hat SEO techniques.

In competitive sectors it may be very difficult to get listed in the top few results for competitive phrases. This is when PPC may have to be used, although this can be expensive in a competitive sector.