Expanding foam behind drywall?

[Wehlen.M]

My in-laws had some people at home fixing their bathroom, Swedish company but Latvians/Poles doing the work. They took the opportunity to install a smaller door to get a larger wall section in the bathroom, and when they installed drywall it seems they used foam sealant behind the drywall panels.

Does anyone know why?

 

[Oddbod]

Probably because there was a narrow gap between the old and new rule. Easier with foam sealant than inserting insulation.

 

[Wehlen.M]

Probably because there was a small gap between the old and new rule. Easier with foam sealant than to put in insulation

Of course, that's the reason! Didn't even think that far, thank you!