[filoleg]

>I wonder how you use them in reality. Learn a new layout for every song?

There is usually no predefined layout (exceptions apply), but more modern controllers with certain software allow you to save your presets and transfer between different projects (kinda like a template).

Normally, it is like a giant chessboard, and you map synths/samples/etc. individually for every new project. So if you are used to having all drums in the top right corner, you can just assign them there on this controller.