I believe it only does sponsors by default, and some categories (like filler) are not shown at all by default. If you never went into the settings, you'd never know.
You can ask Blab (one of two maintainers of the SponsorBlock browser extension and database, the other being Ajay) why not all categories are enabled by default.
There is also a joke branch of the extension called SponsorLock, that isolates sponsors instead of skipping them: https://giveup.ajay.app
There is also a joke branch of the extension called SponsorLock, that isolates sponsors instead of skipping them: https://giveup.ajay.app