Multimicing saves money for the recording company because various screwups that ought to be corrected, and the music replayed, can be patched up (sort of) in the mixing process. It costs a fortune to "rent" an orchestra, so you want to get it done ASAP.
The ultimate multimic situation occurs when one musician isn't even playing at the same time and place as the rest of them. For example, if the concert hall does not have an organ, this part can be dubbed in later by an organist wearing earphones.
The sound tack of the movie "Sweet Dreams" (life of singer Patsy Cline) is interesting. Patsy was in a sound isolation booth (with earphones) when she sang, so her voice is on a completely separate track of the master tape. This made it possible to mix her in with better audio quality accompaniment than that on her original records.
The ultimate multimic situation occurs when one musician isn't even playing at the same time and place as the rest of them. For example, if the concert hall does not have an organ, this part can be dubbed in later by an organist wearing earphones.
The sound tack of the movie "Sweet Dreams" (life of singer Patsy Cline) is interesting. Patsy was in a sound isolation booth (with earphones) when she sang, so her voice is on a completely separate track of the master tape. This made it possible to mix her in with better audio quality accompaniment than that on her original records.