hi mate, i assume your question is for people who have a lot of SP to power down or are buying enough steem/sbd to power up. I am powering up everything i earn.
i feel quite stupid posting to this post of yours, since my objective to increase the steem power that i have and invest in myself and that means my perspective is not truly relevant to your post/question.
However, given the state of crypto markets and where steem is trading both in usd & wrt to btc, i would think accumulating and powering up is the way to go, earn more by upvoting and curating and then when market seems to be in uptrend, start to power down and sell as the market moves up (in case you want to sell).