On all 3D software I used ( Octane, Blender ), I was able generate normal with noise generators. I find this very useful to create materials in the engine and instantly see the result. I like to use noise to make flat surface more realistic : little bumps on painted walls, deformations on windows, large and subtle deformations on a floor or metal, bumps on a plastic surface, dust… A pregenerated texture wont give me the liberty to create the perfect bumps. A lot of objects have noise like deformations. Also, normally with the generator you can generate checker board, marble, sine waves, fractals, circles…