Far superior in what sense?
I know this was not addressed to me but since I feel the same way, I'll mention a few.
It will add strength to the body panels and further reduce noise.
Spray foam will cover and seal all corners. voids and cracks.
It adheres directly to the body panels and pillars and can be sprayed to the depth of the pillars whether that's one inch thick or 4" and once dry, excess that expanded beyond can be cut off. This will give you maximum R value and practically eliminate condensation.
Sheet foam is flat and fairly rigid. Body panels are usually slightly curved and have additional cross bracing and other aesthetic bends. There no doubt will be an air gap between the body panel/skin and the foam sheet. Unless a sheet is perfectly sealed by can foam on all sides, the air in that gap (between foam and skin) will either heat up and rise and be replaced by cooler air at floor level or cool off and sink being replaced by warmer air from the ceiling area. This is called convection and can be a awesome principle to passively heat a home...