The benefits of high SP
With more Steem Power you have more influence on the Steem Blockchain. Thus, you will be able to give out more money in form of cryptocurrency to either yourself or other users in form of upvotes. From the upvotes you hand out, you will get curation rewards (max 25%, but usually 13%) which will also be higher with increased SP.
Bonus
If you have a lot of SP and get somewhere close to the whale club. You will get a lot more engagement and upvotes on your posts because users will expect you to upvote them back.