Search Engine Optimization (SEO) can be defined as the process of increasing the rank of a web site for search engine results while a specific key word is being searched, therefore to increase the volume of traffic to the web site. The higher the website gets ranked the greater the probability of the site being visited.

Strengths & Limitations of SEO:

Cost effective:
No per click charge. So for highly popular keywords, it may be cost effective. Only SEO company will charge their fees.

Credibility:
Most of the visitors arrive at a website after finding it through search engines. So if your site is listed on top of search results, online users place a higher amount of trust in your site. Therefore it is easier to convert those visitors into customers.

Click through rate:
Nearly 70 percent of Internet users click on natural listings, versus 30 percent on paid listings. Organic links are perceived as unbiased, therefore more credible than paid links. Moreover, organic search results gather up to six times more clicks than paid advertising.

Visibility:
Natural listings are more visible than the paid listings on right side of a page, when results showed while a specific search was made.

Limitations:

Limited targeted keywords:
There is a limit to the number of search terms a website may target in accordance to the number of pages involved. We cannot focus on more number of keywords as in PPC.

Time consuming:
Time to get your site listed on top of the natural listings depends on competitiveness of your targeted keywords, age of your website, quality of the content etc. therefore takes time to gain good rankings in the natural search listings and bring traffic to your web site.

Geographic targets:
Its difficult to place your site on top position only for particular geographic location where your targeted customers are located, as the results displayed for a specific keyword will be same all over the world.

Flexibility:
SEO does not give flexibility as with PPC such as landing page, speed, multiple ads and geographical targets by IP location.

When to use SEO:

SEO is suitable for

Those websites whose business requires global promotion, not confined to any particular geographic location.
Those who require long term visibility and can wait a bit of time to see their website listed on top of the natural search results for specific targeted keywords.
A well designed website with a good content will get more profit out of SEO compared to PPC.