"I just wanted to let you know that Ben has been so great with us. I know we were picky (to say the least) before/after our new site went live, but Ben was responsive the whole time. He continues to help us out with website stuff and we really appreciate everything he has done! Also, Chris has been wonderful with SEO stuff as well. He has been very helpful with the SEO project and helping me not let things fall through the cracks. You have a great team and we have enjoyed working with them!"
So we want Googlebot's spiders to be able to come to this page, to understand the content that's on there in a text readable format, to understand images and visuals or video or embeds or anything else that you've got on the page in a way that they are going to be able to put into their web index. That is crucial. Without it, none of the rest of this stuff even matters.
While SEO allows you to optimize your website for a greater chance in appearing higher in search results, and online advertising allows you to send promotional content to the target audience of your choosing, SEM combines both benefits as your content is both optimized for higher search rankings and is placed primarily in front of audiences who are most likely to convert when they click on your ads.