So What are the Benefits?
The benefit of overdubbing is that it allows the each individual part to be focussed on and perfected to the artist and producer’s taste. This requires a lot of discipline and can sometimes lead to performances that are technically perfect, yet sterile and lifeless. It’s not natural for musicians to perform individually. This is why a tracking session requires the whole band to perform together. The drummer needs something to respond to in order for his/her performance to sound “live” and not programmed.
Overdubbing is a very difficult thing to get right. Because of the lack of visual cues that would normally lead a performance from one section to the next in a song, the musician has to record their part blind against the prerecorded band. Subtle pushes and pulls in a performance that may be conducted by subtle visual cues of the other musicians now disappear. The overdubbing performer is then left to guess or adapt their performance to match what was captured in the tracking session.
This has naturally led most multitrack productions to the use of click tracks which even out the tempo of the tracking performance. With a click track, the overdubbing process is less of a guessing game and more of a known quantity. Because of the difficulties overdubbing presented in the recording studio, musicians who were good at it became hired guns to quicken the production process. Many musicians have made very successful careers only working on other artists recordings in the studio.