>>3775518>Game makers from other companies had ignored the tech manuals and jumped directly into the ROM. They had no reason to care.Using the jump table induced an extra JMP instruction, which took more CPU cycles to execute. If you're running a tight loop or have to count your cycles to meet exact timing requirements, as was the usual case in these systems, you would have to trim off whatever extra you can.
The "Useful code" was the C64's operating system, providing functions like reading the keyboard, mouse, memory allocation etc.
