Really only the latter is useful and the former is mostly wasted cycles except for dealing with language beginners and eccentrics.
Recently at work we adopted Prettier to avoid having to deal with things like line-lengths and space-based tab sizes. Running Prettier over the codebase left us with terrible-looking cramped two-space tabbed code but at least it was consistent.
However having started to live with Prettier I’ve been getting less satisfied with the way it works and Prettier ignore statements have been creeping into my code.
The biggest problem I have is that Prettier has managed its own specific type of scope creep out of the formatting space. It rewrites way too much code based on line-size limits and weird things like precedent rules in boolean statements. So for example if you have a list with only one entry and you want to place the single entry on a separate line to make it clear where you intend developers to extend the list Prettier will put the whole thing on a single line if it fits.
If you bracket a logical expression to help humans parse the meaning of the statements but the precedent rules mean that brackets are superfluous then Prettier removes them.
High-level code is primarily written for humans, I understand that the code is then transformed to make it run efficiently and all kinds of layers of indirection are stripped out at that point. Prettier isn’t a compiler though, it’s a formatter with ideas beyond its station.
Prettier has also benefited from the Facebook/React hype cycle so we, like others I suspect, are using it before it’s really ready. It hides behind the brand of being “opinionated” to avoid giving control over some of its behaviour to the user.