Most spray on foam insulation I have run into is just a flash coating on the exterior walls that is not really that thick, maybe up to an inch thick, with occasional places that were hit more and are thicker. The idea is to seal everything with this relatively thin coat - but it has essentially no holes or gaps so it seals well. This is the vapor barrier and they don't put the traditional plastic vapor barrier up that used to go right under the drywall if it was flash foamed. They then fill the rest of the stud cavity with other traditional types of loose fill insulation which I'm assuming costs less or they probably would foam the whole wall. Often it is same company foaming as well as installing the loose fill, maybe not the same crew for each part but same company.
If you have a good crew they tape over your wall boxes so they don't get foam in them, though if they do get foam in them it usually is not intentional and is not all that much.