The end result can look 'muddy' if the conditions aren't right and you stack more than 3 or 4.
The old way was to do a photomontage with the neg. There were guys who could strip out the three layers of a colour film, montage various bits of neg or tranny together, retouch and the finished result would have fooled anyone. I worked on a car shot where we took five different shots in four different locations and the image was assembled in the lab. Even I had a hard time seeing the joins.
But those guys got paid a heck of a lot more than the photographers did.
The other way, as I have said, is to use mattes inside the camera.