While joining and actively participating on Steemit. This platform reward us in form of Steem, Steempower and Steem Dollar. These three combine determines worth of our accounts/ wallets. Steem and Steem dollar can be traded on exchanges and also be converted into Steem power.
Steem Power determines the voting power of the user. Thus enables us to earn more through curation and if someone don't have time to upvote for some reason he/she can also delegate your voting power to someone in need and in return you are earn money. However, my point of view is that one should also spend some time on steemit and contribute towards the community and also earn through it.
While Steem or Steem Dollar in one’s account can’t earn anything, if it remains in the account. The only way to increase or decrease in its value is through value of cryprocurrency.
So in my opinion one should invest in Steempower as you can get extra income even if the proce of steem does not increase. The only problem in investing in Steempower is that it takes 3 months to liquidate your Steempower back to Steem.