Moisture block, not just insulation. Closed-cell foam cures into a dense rigid material that does not absorb water. Where fiberglass batts turn soggy and grow mold after a single roof leak, closed-cell stays dry and keeps insulating.
Built-in vapor barrier. At two inches or more, the foam acts as a Class II vapor retarder on its own. You get insulation and vapor control from one material, which matters when your outdoor dew point is in the 70s for months at a stretch.
Mold has nothing to feed on. Mold needs moisture and organic material. Closed-cell foam provides neither. It does not give mold the food source that paper-faced batts or exposed wood framing can.
High R-value in tight spaces. Roughly R-6.5 per inch, so closed-cell delivers real thermal performance in attic rafters, crawl space walls, and rim joists where you do not have room to stack several inches of lower-density material.
Structural reinforcement. The foam bonds to framing and adds racking resistance to walls and roof decks. In hurricane country, that quiet structural contribution is worth having.
Resilient after storm exposure. If water gets in during a tropical system, closed-cell foam dries out and keeps working. You are not looking at a gut-and-replace job the way you would with wet fiberglass.