My opinion is that it's a mix of benefits and drawbacks, depending on whether you're a voter or an author.
I think the main reason people promote powering up is that when more STEEM is powered up, that means the supply of liquid STEEM is lower, which should drive up the price of STEEM on the exchanges.
I don't know if that has been empirically demonstrated, though, and it's a little like playing "musical chairs", because you don't benefit from the higher prices until you power down.
Additionally, I think a couple less favorable side-effects are that when more STEEM is powered up, the interest rate goes down and there is more competition for curation rewards.
On the other hand, for authors, I guess if more people power up more STEEM (and use it for voting), it's probably easier for your content to get found and rewarded.
Personally, I like to keep an eye on it because I think it reflects the confidence that people have in the blockchain.
RE: Steem Total Value Powered Up - $67 million - August 6, 2021