Throttles are for setting the delays associated with interrupts and how often the emulator releases control to the OS. 

T 2 4 R D

T is CPU
2 is SN2661
4 is MVME400
R is RWIN
D is Display

good working initial values are CPU=1024(10) 2661=4096(12) 400=512(9) RWIN=128(7) DISPLAY=0(0)

CPU throttle causes the emulator to release to the OS every x micro-instructions. 

2661, 400 and RWIN specifies how many intructions should pass after a funtion is done. this delays the actual interrupt for that many instruction, allowing for the interrupt to be serviced before another occurs.

Display simply specifies how often the emulator releases control during display of characters on the screen.

These must be set approprately, else an OS may crash due to tight interrupt situations, where there's not enough time to service and handle the interrupts. Versados may crash if the Background activation table fills. Unix may toss characters if the input queue is full. 