Traditionally I have always mounted just the filesystems I needed in single user mode whilst tinkering in Solaris. Turns out this is a dumb method for ZFS filesystems.
What happens is that the zfs mount command will create any directories necessary to mount the filesystem. Later this can stop other ZFS filesystems from mounting when the tinkering is finished. This could be an argument for not creating hierarchies of filesystems, but that’s rather extreme.
The better solution is to mount all the ZFS filesystems in one go with :-
zfs mount -a