SEM vs. SEO
Generally, "search engine marketing" refers to paid search marketing, a system where businesses pay Google to show their ads in the search results.
Search engine optimization, or SEO, is different because businesses don't pay Google for traffic and clicks; rather, they earn a free spot in in the search results by having the most relevant content for a given keyword search.
Both SEO and SEM should be fundamental parts of your online marketing strategy. SEO is a powerful way to drive evergreen traffic at the top of the funnel, while search engine advertisements are a highly cost-effective way to drive conversions at the bottom of the funnel.
Do I need Both SEM and SEO?
No. But will you end up getting a lot more leads and sales if you implement both? Absolutely yes.
It's always a good idea to optimize your site according to SEO best practices. You want to lay out a solid foundation that will put you as far up in the SERPs organically as possible. After all, SEO clicks are basically free—why wouldn't you want as many of those as you can get? Utilizing search engine marketing, however, can significantly speed up your ability to build your brand and your client base. It will put you in front of target audiences who are actively searching for products, services, and brands just like yours. You want to appear at the very top of their searches, or someone else will get their sale.
So, Which is Better? Strict SEO or SEM?
Advocates on either side could argue one is more effective than the other, but I like to view high-quality SEO as a prerequisite for high-quality SEM. SEO lays the foundation for SEM through well-optimized content that prospects and customers find helpful. Without landing pages, web pages and blog content optimized for search, your SEM efforts will fall flat due to poor quality, and visibility in the SERPs will be extremely difficult. Organic SEO is also less costly long-term as you establish search credibility, as long as you maintain it with the consistent creation of quality content and social media usage.
On the other hand, if you're just launching your first website and initial online footprint, you're likely going to need some immediate visibility in search until you build up some organic credibility. With a strategic PPC campaign, you'd be able to achieve this. What you shouldn't do, though, is rely strictly on PPC long-term while ignoring organic SEO.
So, evaluate what's best for your specific needs but make sure you fully understand the differences and how you'll maintain your efforts long-term.