They're not necessary, but it's a nice thing to have. On a level of a single binary, you can prove that the program you have has been built from a corresponding

They're not necessary, but it's a nice thing to have. On a level of a single binary, you can prove that the program you have has been built from a corresponding source code (no backdoor included). Which is very important if you want to increase the security of your supply chain (most people won't compile signal from source, for example).