I do have not any experience with the NDA's in the music industry, only as an engineer and those NDA's were for protection mostly towards patent intellectual property (IP) and trade secrets.
As a mechanical design engineer, I've had to sign many of those NDA's. Mainly, the company is interested in protecting their intellectual property they hired the engineer to develop. This is the part that makes sense and the way it should work. The company hires the engineer, programmer, or businessman to develop a product, apparatus, method, software or business method, and they want to be able to bring to market. The company paid for the research in the first place.
A company may also want to prevent their competition from gaining an insight about the companies business. Many times the company will rely on “trade secrets” to prevent their competition from finding out about their workings. “Trade secrets” do not offer the same protection that a patent, trademark, or copyright will give. But, “trade secrets” will afford some protection. The patent will expire in 20 years, and there is no renewal unless the company is able to come up with another patent that uses the parent patent in such a way as to give them some exclusive rights. A patent is also published and open to the public, so there is no secrecy, unless the patent is classified for the government or military.
Sometimes a worker will be given the NDA to sign to prevent the worker from working in the same industry. That will stop some workers, but not professionals in fields, and where the employee was hired because of their previous experience in special fields.
The NDA’s in this case protect companies from loosing their trade secrets to their competition. But, sometimes the NDA's go too far when the company sees an opportunity to cash in on any intellectual property that an employee may have been working on outside the company time and location, regardless if it had any relation to what the employee did for or with the company.
I was hired for one company, many years ago, that had their NDA so broad that if I wrote a fictional novel or wrote a song, they wanted to gain profits from just me being allowed to go through their front door to work everyday. This company, wanted to go far beyond the IP for patents. They wanted to extend their control to IP that may have been related to art, music or novels. They could not prevent me from working in engineering, because I had previous experience and education prior to my employment.