To put it simply, SEO (Search Engine Optimization) is one of the most important knowledge/skills that all internet marketers should be aware of. Having said that, since time is money (correct in both online and offline space), many internet marketers would preferred outsource their SEO needs to specialists.
This is especially true since global search is still on the upwards trend even with the "invasion" of social networking sites (like Facebook, Twitter and Pinterest etc..) and there is no sign of slowing down. Thus, if you do not want to spend too much time and money on the paid search result, do spend sometime on the on-page and off-page SEO (of your site/blog) either by yourself or through SEO service provider. One of such prominent play is MOZ.
Lastly, check out the following relevant Infographic: