[Canada]

I go for constraints every time. Data Integrity is king as long as you can reasonably afford it.

Your data migration aborted on an unexpected error? Well in my view that's a problem and you need to figure out why that is happening and fix it.

But hey, you can always drop the constraint when you decide it's not worth it, and you can always add it back again after. Depends on the application too, sometimes it just doesn't matter if you make a mess.