There are many Search Engines that people browsing the Internet are likely to use. Each Search Engine has a robot, or software, that travels the Internet and indexes each page it finds. Each Search Engine indexes these pages slightly different and they also return the information to the browser slightly different as well. It is important that you plan for these Search Engines before you build your Site. If you don't it is still highly likely you will be listed at the Search Engine but what good is it if you are listed on the tenth page of the results each time.
Nobody goes that far to see what 's there.
You want to be listed in the first couple of pages of search results. Yes, you could do this after you build the Site but you would in effect be redoubling your efforts if you found your Site did something that your Search Engines of choice didn't like. But I don't know how Search Engines work. You don't have to know. We at Informulation can take care of optimizing your Site.