It's a basic question, and what you'd think is that it's straight forward, that it doesn't matter.
But it does!
Contrary to what I originally believed, there's no real benefit to doing a power up post, as the steem power is distributed at the current market price rather than a flat rate.
So what does this mean?
Essentially the only purpose in powering up directly is if you want the cute squiggles next to your post, or if you don't care about the minor things and just want steem power. But even then you shouldn't just power up all the time.
Why?
This guy right here.
@Randowhale will give you the highest ROI (if you're a greedy fuck) if you use SBD rather than Steem Power, meaning that 50/50 rewards may be more desirable if you want to toss some money into him for your own posts or others.
Other than that you can penny pinch and cash in your SBD for steem when the market is low for a small benefit I believe, but it really doesn't matter all that much.
Personally while 100% of what I "earn" will go back into steem for the foreseeable future, and the community, I'm not going to be powering up all of my posts anymore. I'd like to start shooting 
I'd suggest you to do the same, although really it doesn't matter all that much, but it does a little :)