Paid or sponsored ads usually charge you for a click, while SEO doesn’t require you to pay for impressions or clicks. But do keep in mind that quality SEO isn’t exactly free. Depending on the target market you are in, you will have to invest time and money into getting the desired results. And if you’re not an SEO expert, then you would have to work with a reputable SEO company do it for you.
The one thing i had on my mind outside of this list is keeping websites organized, somewhat simple, and pointing value to the right places. Britney's removal of thousands of low-quality pages that delivered results were an indicator of the importance of this. Google realizes that a few years back folks were just creating content thinking it would get them ranked, and their indexes were getting populated with pages that were worthless. I think organization and tidying up outdated posts/pages on sites will be rewarded.
Thanks for the helpful information discussing the differences and similarities between SEO and SEM. The information was enlightening because a search engine optimization company like the one that I own is relatively new at starting. We believe everyone should always check out their sources because every different perspective is very different so all approaches can be understood differently.