you can get two benefits by adding blog into your site. (1) content can be increased with the passage of time and those could help fix content to rank up. (2)blogs are primalarly SEs friendly, so that no need to optimize. Blog can be favorable, if it uses in a right manner, like urls must be SE friendly, content must be unique, no link farming, don’t use your blog for link building, if you have better contents, people wants your link to be placed on their sites. So overall blogging is a way to enhance site content and let the crawlers to visit frequently.