If you hold your 100 Steem in you Bittrex account, then in 2 years you will still have 100 Steem. If you Power Up your 100 Steem now, then in two years you will have approximately 400 Steem. Powered Up Steem doubles every year (not quite double, something closer to 1.86x if I remember correctly, but close enough to be double).

Also, even if you do not blog, you can still earn rewards by upvoting and commenting thers blogs. The move Steem you have powered up, the greater your rewards for commenting and voting.

So definitely power up if you are going to hold the Steem long term.