Being able to enter a debugger on NMI is great because now you can trigger the NMI from any set of hardware conditions too - you can connect logic gates to the

Being able to enter a debugger on NMI is great because now you can trigger the NMI from any set of hardware conditions too - you can connect logic gates to the address bus to decode a range of addresses, "and" it with the memory write assert pin or IORQ pin and now you have hardware breakpoints for a machine that didn't originally support it.