Running fstrim as cronjob - what happens when interrupted by shutdown

One of the ways to implement fstrim on a file system, it to make a cron.daily task that runs fstrim /. This is preferred over -o discard (mount option) by a lot of people, because the latter can make writing slower, especially deleting large amounts of small files.

My question then is, when I do make a cron job like that, what happens if this gets interrupted by a reboot/halt, or worse, a power loss? SSD's don't like power losses to begin with (there is even a SMART parameter to count them), and I can imagine that power loss during fstrim is even worse.