The worst thing that happens is when the former social media manager gets fired, is totally p#$$$%^ off and changes all the passwords and then refuses to hand them over. This can literally bring your business to its knees! And this happens a whole lot more than hacking.
Search Engine Optimization (SEO) organizes the pages on the website for both the search engine spiders and the visitors to the site. Search engines look for your site based on combinations of words on the site. The more words you have on your site, the easier it is to find. That's why a blog is so much more effective than a static webpage.