What happens if my roof leaks?

With “Closed Cell” spray foam the leak will never come into the structure because the material is not “hydroscopic” (doesn’t absorb water).  So if you get a roof leak, the water is sealed outside of the building envelop.  Most other forms of insulation (including “Open Cell” foam, fiberglass and cellulose are hydroscopic (absorbs water) so the leak will enter the building envelop, and may rot out the roof sheathing.