Without getting technical on the SEO specifics, the most simple way to understand the impact of SEO techniques can be looked at by assessing two things:
1.) What SEO, in all shapes and forms does for your website.
2.) What value search engines, specifically Google wants to see from your website.
On the first point, SEO should generally focus on painting a prettier picture in terms of usability, accessibility, contents, and deliver an easily recognized solution for the visitor. This should absolutely include changing up and adding fresh content to keep your website relevant and “solution/resource” oriented for the searcher.
On the second point, ultimately search engines see users/searchers as “customers” they want to provide the most adequate advice and results for their customers.
In a nutshell, when gearing up the SEO or content direction for your website whether this be in the form of optimizing images, titles, page content, target phrases etc. The biggest factor you should consider is ensuring you are bringing adequate value to the visitors you are targeting.
Adding SEO tactics into your website as well as offering up fresh contents for your viewers will help in your overall SEO mission. You just want to make sure you are looking out for what the search engines want to see along with making an effort to satisfy their perspective as well.
Search engines always want what is best for their users, so if you can add targeted content while following compliant standards within your website and page contents, you should be in good shape.