It is important to understand that Steem dollars and Steem power derive all of their value and power from the value of Steem which is the fundamental unit of the Steem blockchain.
The value of Steem is constantly being diluted since there is an automatic 100% supply increase of Steem per year. For this reason, you will want to convert your Steem to Steem dollars or Steem power.
Steem power is a unique system that is used to inspire long term growth and commitment. The cryptocurrency world is known for investors jumping from one cryptocurrency to another depending on the trend of the moment. Bitcoin is perhaps the most well known cryptocurrency. While Bitcoin has maintained its value, many crypto currencies fluctuate wildly. I have personally been involved in Dogecoin which has seen wild fluctuations due to investors jumping from one currency to another.
Steem power is required for voting on content on the Steem platform.You cannot withdraw these funds whenever you want.
If you have 10,000 Steem Power, you can cash out for 10,000 Steem over 104 weeks equally divided.
If you believe in the platform, you should get Steem Power.
Steem is the base currency of Steemit.
It is designed for speculation. This is the only 1 of the 3 currencies that can be traded on exchanges like Bittrex.
Steem is used to buy Steem Dollars and Steem Power.
The quantity of Steem doubles every year.
In most cases, due to the inflation of 100% per year of Steem, you'd want to hold on to steem no longer than 10 days (otherwise, the built in inflation is devaluing your Steem by 0.19% per day)
Always buy Steem, as this is what you need to buy everything else. Steem inflates at 100% per year. So if there is 1 million Steem available in the world at the end of 2017, there will be 2 million Steem available in the world at the end of 2018. This is the only currency of Steemit that you can trade on exchanges like Bittrex. The price is volatile, so traders might like this to do do buy/sell trades for profit.
Steem Power will make your upvotes on Steemit more powerful, giving you influence on this platform. Steem Power is for the believers of the Steemit platform.
The benefit of holding Steem Power is that you're more powerful on Steemit and you earn somewhere around a 90% interest per year in the form of Steemit.
Buy Steem if you want to do some trading, buy Steem Power if you believe in this platform.