FUSE is neat for one-off access to obscure file systems, and FUSE is usable for things like sshfs for those who use that, but it is my impression from having used FUSE myself that FUSE does come with a noticeable performance penalty. Is my perception wrong on this? Because if it is not then I’d be hesitant to use a system where the main storage was relying on FUSE.

FUSE is also great for slower media. Copying files over USB sticks without being restrained by FAT-32 limitations is great. There have been times that I've used NTFS-3g for this because its FUSE implementation meant I could read it on any OS.

Stuff like gocryptfs seem to push FUSE to quite high performance. There is still some latency but streaming read/write seem to go fast.

Do you have any documentation on that?

The benchmarks on their website[1] compare it running on a 4 x 3.20GHz with hardware AES-N instructions, against an in-kernel implementation of a different cryptosystem running on a 2.7GHz cpu that does NOT have AES instructions. I also can't see anything that speaks to speed of the storage (or if this is controlled for), so I'm admittedly quite skeptical.

The numbers they do publish aren't particularly impressive to me either, so we may also have wildly different ideas about what "quite high performance" even means.

[1]: https://nuetzlich.net/gocryptfs/comparison/#performance

This is also how the original BSD UFS/FFS was developed some three decades ago.