CGI can either be 100% CGI where the surrounding context is not clear or relevant to the final views, or a photomontage to blend in with a photo of the existing area.
Interior 100% CGI
Every stich and crease needs to be modelled before the lighting and texture bring it to life.
Close up views
Once modelled small vignettes can be produced to act as fillers in brochures or editorial.
And the camera can be repositioned to produce another view of the same room, without doubling the cost.