Edit: reasons added in because I can’t read the post title
OpenBSD laptop: ffs2, vfat for efi system partition
Why: Contrary to popular belief, OpenBSD does not support zfs. The only other filesystem options are msdos (fat family), and ext2fs (mostly for Linux compatibility as far as I can tell, filesystem is experimental and lacks a bunch of features according to the manpage). Makes ffs2 the only sane option.
Why: I prefer not having journaling on flash memory. This hasn’t bitten me in the ass too hard yet, and even when it does I can usually get around system files being lost with integrity tools. Maybe I’ll dabble with f2fs some day, but I’ll need to read about its features and shortcomings compared to ext2.
Alpine Linux VM: ext4
Why: Would have installed as ext2 as well, but I forgot