can't agree more as somebody who joined a place for the sole purpose of maintaining already profitable products and continuously pay the tech debt there.
I keep emphasizing it, looking at this project is like looking at a complied code, you can understand what this portion does by reading the program but You can't understand what the dev/architect had in mind when they did it, architectural diagrams + proper high level docs can do wonders. I can understand what those modules are doing, but it will take me years before I can grasp the entire system to know where to look for every fix/new increment.
I keep emphasizing it, looking at this project is like looking at a complied code, you can understand what this portion does by reading the program but You can't understand what the dev/architect had in mind when they did it, architectural diagrams + proper high level docs can do wonders. I can understand what those modules are doing, but it will take me years before I can grasp the entire system to know where to look for every fix/new increment.