Yes, because this will help you to understand your competitor SEO strategy. And also help to know how you will be implement this strategy for your website to get high rank on google.
In off page SEO we perform link building ,social media and social bookmarking. Off page SEO give indication to increase the websites ranking.
Competitive analysis of keywords is necessary in order to get an idea how much traffic can be generated from the targeted keywords and what keywords are used by competitors to reach customers so that it would be beneficial for your website too.