SEO in the development process
Ninety five percent of the time, Search engine strategy is thought when the website is already coded and live. Then the company that runs the website starts to wonder "Hey! we got the best website in the world... why don't we make any business with it??"
Well the answer is quite simple, "NOBODY FINDS YOU!". You can have the sexiest website in the world and be the best expert of your area, if nobody knows it ... you won't do any business.
Search engine optimization is a lot easier and cheaper to implement when the strategy is thought before the webiste is developped.
Wrong Web development process
In the above process, SEO is implemented after the website is launched (or even worse RE-launched). As a result the website won't acquire a good visibiliy from scratch, the optimization is going to require some code modifications and some additional budget. In an nutshell, YOU DON'T MAKE AS MUCH BUSINESS AS YOU EXPECTED AND YOU EVEN NEED TO SPEND MORE MONEY TO CORRECT THINGS.
Good Web development Process
In the above process, Search engine marketing strategy is set up before the website's launch (or relaunch). As a result, the website is search friendly from scratch, the website acquire some visibility, traffic and customers quickly.
In teh case of a website redesign you MUST think about search marketing strategy before lauching the new version of the website as it will prevent a massive loss of visibility and traffic due to the modification of the URLs.